As the dust settles on season five, Arrow has us more excited than ever for the post-flashback era of the show. In passing 100 episodes and launching its first four-night crossover, the fifth season has hit two major milestones on its way to lifting Arrow from the murky waters of season four.

A fair chunk of the show's 100+ episodes have been permanently wiped from memory as we all try to forget seasons three and four, and even the rest have trouble shaking the show’s forced flashbacks and inconsistent character development, but it’s still difficult to fathom where we’d be in a world without Arrow.

The show is almost solely responsible for bringing us The Flash and Legends of Tomorrow, with Black Lightning also on its way in 2018, while the likes of Supergirl and Constantine are now officially included in Arrowverse canon. Considering how much it has given superheroes on mainstream television, there’s even an argument to be made that Daredevil and the rest of the Marvel Netflix shows owe their success to Arrow.

With that in mind, let’s count down the episodes that take credit for the show’s phenomenal success. Here are the 15 Greatest Episodes of Arrow.

15. “The Scientist” (2x08)

Arrow "The Scientist"

It’s no coincidence that the lightest episode in Arrow’s entire run just so happens to be Barry Allen’s Arrowverse debut. Pre-lightning bolt Barry is a bumbling mess, always turning up late and way too young to be investigating anything, which is referenced several times by Oliver: “Do your parents know you’re here?

The humor in “The Scientist”, between Oliver’s snarky remarks and Felicity’s approval of Barry, does just enough to distract from the introduction of metahumans and super soldiers to a show that was once so grounded. The League of Assassins also gets a mention, as Moira brilliantly gets one over on Malcolm Merlyn in the background.

The episode uses Barry Allen to very subtly embrace its wider universe, but at the same time remains grounded as Mirakuru soldiers begin to surface in the present.

14. “The Calm” (3x01)

Arrow "The Calm"

To put it lightly, season three isn’t a favorite among Arrow fans, but most of its criticism is down to the mystical and metahuman elements the show was forced to embrace in the wake of the Flash’s arrival. “The Calm” is actually a strong season opener, with shades of the much more realistic second season still looming over Starling City, and the introductions (and reintroductions) of several characters.

Count Vertigo comes back under new management, leaving the absurdly campy version of the character firmly in the first two seasons. Amanda Waller returns in flashback form, long before the Hong Kong arc lost its way, and Sara resurfaces, to be immediately killed and remind Oliver that rebuilding Starling is a long way off.

The real highlight is the fresh face of Ray Palmer, who injects some much needed levity into an episode that is dark even by Arrow’s standards.

13. “Vendetta” (1x08)

Huntress and Oliver on Arrow

In the early days of the show, with fans still waiting for Black Canary to make her debut, it was actually the Huntress who became the first Bird of Prey introduced to Arrow. Helena Bertinelli was Oliver’s first love interest after resurfacing from Lian Yu, and she remains an influence on how Oliver goes about balancing his two lives to this day.

As their human connection grows stronger, Helena’s vendetta toward her father reaches breaking point, and the pair makes enemies of each other’s alter egos. The Tommy and Laurel subplot actually works in this episode, offering an insight as to how their relationship might have panned out if not for Oliver’s vigilantism.

It’s the first time Oliver had been open about his crusade, so Helena’s betrayal only makes it more meaningful when he allows Felicity, Roy, Thea and Laurel into the Arrow Cave.

12. “Pilot” (1x01)

Oliver Queen pointing a bow and arrow during the Pilot episode of Arrow

This is the one that started it all. Before metahumans and aliens, before that time in season three where just about every character on the show died and came back to life in a magical pit, there was the pilot. Back when things were grounded in reality, the very first episode of Arrow reminds us all of a simpler time.

It does everything you expect from a pilot, setting up Oliver’s motives and relationships with the rest of the cast, but its dark undertones and unique take on flashbacks (which we swear were interesting at the time) gave us something we’d never seen from a superhero on TV. Five seasons later, the show is still relying on exactly the same formula, and so are the three other CW shows for which Arrow takes credit.

11. “Legends of Yesterday” (4x08)

The characters of the Arrowverse standing together, including Legends of Tomorrow, Arrow, and The Flash.

No one who watched the pilot in 2012 could have predicted the turn out for this season four episode; the only season four episode, not coincidentally, to make this list. Of the major crossovers, “Legends of Yesterday” is arguably the weakest, with an Oliver/Felicity break-up subplot that feels out of place amid a crossover event.

Still, that doesn’t take away from the core team-up of Green Arrow, Flash, Hawkman and Hawkgirl. Also, the benefit of having Barry Allen around in these situations is that the unnecessary relationship drama can be quickly reversed. On a side note, Barry made his Arrow debut exactly two seasons before, and it’s remarkable to see how far he has come as this episode unfolds.

Barry travels back in time to prevent the destruction of Star City and the murders of his friends at the hands of Vandal Savage, who comes across as more of a threat in this Arrow episode than he did in the entire first season of Legends.

10. “The Odyssey” (1x14)

Arrow "The Odyssey"

A major factor in the success of Arrow’s second season was the relationship Oliver once had with Slade Wilson. If ever an episode showcased their budding friendship, and in hindsight, makes it all the more brutal when Slade descends into villainy, it’s “The Odyssey”.

The season one episode takes places mainly on Lian Yu, with Felicity briefly teaming up with Diggle to save a weakened Oliver in the present. Felicity’s introduction to the Arrow Cave keeps the modern day storyline ticking over nicely, but it’s the character development in the past that makes the episode stand out.

Slade begins training Oliver, who delivers one of his few genuinely comedic lines in five seasons of television: “I’m stranded on an island, and my only friend is named Wilson.” It’s a tragic relationship, knowing the direction in which Slade is heading, but “The Odyssey” sells the impossible idea that Oliver Queen and Slade Wilson might have been friends.

9. “Deathstroke” (2x18)

Arrow "Deathstroke"

Picking a single episode from the season two run is near impossible; “The Man Under the Hood” and “Seeing Red” contain some of Arrow’s most powerful moments, but the episode that came directly before them set the tone as the show closed in on its season two finale. “Deathstroke” is when things really start to fall apart for Oliver and Team Arrow, as Slade finally sets his five-year revenge plot into motion.

Starting with Isabel Rochev’s takeover of Queen Consolidated and ending with Laurel learning Oliver’s secret identity, with a whole kidnapping subplot in the middle, there isn’t time to take a breather through the entire episode. Stephen Amell gives one of his best performances in the green suit, as he slowly comes to realize that his efforts to protect his family are playing right into his enemy’s hands.

8. “Sacrifice” (1x23)

Arrow "Sacrifice"

Season one is held in general high regard, in no small part due to its finale, which was the best Arrow had ever been at the time. The premise is fairly typical, with Oliver collecting what he had learned over the course of the season to defeat a villain threatening to destroy his city, but where “Sacrifice” stands apart is that Merlyn actually succeeds.

Not many superhero stories have the nerve to blow up half the city their hero is trying to protect, but Arrow distanced itself from the rest, and as a result, Oliver took a more measured, less murderous approach that directly inspired later seasons of the show.

Elsewhere, the episode’s action upped the stakes for the show moving forward, with a rooftop fight scene to blow the rest of the season’s set pieces out of the water. And Tommy’s death provides the core of the episode, capped off by a Stephen Amell performance that we hadn’t seen before on Arrow.

7. “Invasion!” (5x08)

Diggle walks in on Oliver talking to Laurel in a wedding dress on Arrow "Invasion!"

The Arrow segment of the “Invasion!” crossover not only had to fill in the gaps between The Flash and Legends, but it had the added dilemma of being the show’s 100th episode. In the end, it uses the crossover to its advantage, trapping its main characters on an alien spacecraft (a long way from the grounded reality of the pilot) and showing us the lives they might have lived if not for Oliver and Sara’s affair.

Laurel, Moira and CGI Tommy return alongside Damien Darhk, H.I.V.E. and a Manu Bennett-less Deathstroke to remind Oliver and company of how much they have lost. Rather to stay in the hallucination, they force their way out in a five-on-five battle that pits each member of Team Arrow against the character that took the most from them individually.

Everything from Quentin’s non-existent alcoholism to Ray’s reintroduction to the Arrow cast makes for a fitting tribute to the show, and Barry and Kara’s real world team-up proves beyond all doubt how far the Arrowverse has come over the years.

6. “The Brave and the Bold” (3x08)

Arrow "The Brave and the Bold"

The first official crossover came two seasons earlier, and as much as we love Supergirl and the Legends, the dynamic between Teams Arrow and Flash is impossible to top. The second and better half of the two-night event, “The Brave and the Bold” welcomes Barry, Cisco, and Caitlin to Starling, where their attempts to lighten up the place are quickly squashed by Oliver and Diggle.

Barry eventually proves his worth to Oliver, twice saving him from Captain Boomerang, and also consoling his once-mentor. Having lost his mother to Slade and Sara to Thea, Oliver is back to using violent means to stop the criminals of Starling, and Barry is the outside perspective he needs to keep him from falling into darkness.

On top of the spectacle of a Flash and Arrow team-up, both characters take a little something away from the crossover, which ends with Oliver stopping Boomerang non-lethally in one of season three’s best action scenes.

5. “Kapiushon” (5x17)

The majority of this list is made up of finales and crossovers, but “Kapiushon” cracks the top five without being either. The way the episode is cut together is strangely reminiscent of an Arrow season finale, though, with increasing inter-cutting between past and present all leading to the same reveal.

Editing counts for nothing if the performances aren’t up to scratch, and Arrow isn’t generally a show that puts performance first. This time around, watching Stephen Amell and Josh Segarra pick each other apart in Prometheus’ holding cell is a real treat, and Dolph Lundgren makes a surprise return to Russia for good measure. John Barrowman even gets in on the act, turning in a flashback appearance to put the finishing touches on an episode five seasons in the making.

The reveal itself, that Oliver enjoys killing, we already knew to some extent, but “Kapiushon” is less about the final twist than it is the overall package.

4. “Three Ghosts” (2x09)

Arrow "Three Ghosts"

Barry Allen is back for the second mid-season finale, which ends with the particle accelerator explosion at S.T.A.R. Labs, but Barry becoming the Flash isn’t even the main takeaway from this episode.

The titular ghosts are hallucinations of Oliver’s past, present, and future, with Shado reappearing in the same episode as the flashback of her death, and Tommy delivering a heartbreaking motivational speech just nine episodes after his own. But Oliver’s future ghost, Slade Wilson, makes his debut in present day Starling, with a hole where his right eye should have been, just as Shado is killed on Lian Yu.

“Three Ghosts” does everything it should in setting up the second half of the season, leaving the past of the flashbacks, Slade’s arrival in the present, and the future of The Flash wide open.

3. “The Climb” (3x09)

Ra's al Ghul holds a sword to Oliver's throat in Arrow

We’ve given season three some stick, but its first half has three solid entries on this list, and it’s all capped off in epic fashion by “The Climb”. The mid-season finale drops one of the most literal cliffhangers in television history, as Oliver battles Ra’s al Ghul in a trial by combat for Thea’s life.

We had barely seen anything from Ra’s up until this point, and the episode does a fantastic job in building up the character, cutting between the past and the snowy mountains of the present. Matt Nable gives a stone-cold performance as Ra’s stamps his authority on the Arrowverse, letting us know plainly that Oliver is going to have to up his game to beat him.

No one honestly thought that Oliver was dead, but no one thought he was going to be stabbed and kicked off a mountain either, which was exactly the right thing to do given Ra’s’ years of experience, and to raise the stakes following the second season.

2. "Lian Yu" (5x23)

Oliver holds Adrian in a headlock in Arrow

Only time will tell how the most recent episode stacks up when compared to the memorable episodes of Arrow’s past, but on first impression, “Lian Yu” is something spectacular. The finale ties up five seasons’ worth of loose ends, as the whole cast converges on the island for a final time.

Included in the line-up are previous villains Merlyn and Deathstroke, which gives weight to the strength of this season’s big bad, as Josh Segarra puts in a performance to rival season two Manu Bennett. After a double-double cross of his own, Bennett’s return to Lian Yu more than anything else reminds us of Arrow at its best.

If anything keeps the episode from the top spot, it’s that Konstantin Kovar (Dolph Lundgren) never ties into the present, which feels like a waste given the character’s build-up and apparent resurrection. But the flashbacks themselves are consistent with the high tempo of the present, as Arrow comes full circle with one of its greatest episodes.

1. “Unthinkable” (2x23)

Slade holds a sword to Felicity's throat in Arrow

The title of the season two finale is appropriate in so many ways. Oliver teams up with the League of Assassins, Diggle and Lyla with the Suicide Squad, and Thea with Merlyn as Team Arrow goes all out in its effort to stop Slade Wilson. It’s Felicity who directly references the “unthinkable”, which leads to Oliver’s plan to bate Slade into capturing Felicity herself.

The finale gives Felicity a major role in an episode that sees everyone else beating up super soldiers, and makes good on her season-long chemistry with Oliver (which hadn't gone stale just yet) all at the same time. After she injects Slade with the Mirakuru cure, Oliver’s climactic showdown with Slade shows exactly how far he has come by cutting seamlessly between their past and present battles.

For a show that uses flashbacks as a selling point, Arrow has never used them more effectively than in this episode, while its present characters are each given an important part to play in Slade’s defeat. Ultimately, the finale does the literal unthinkable, and lives up to an epic end of season run-in.

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Which episodes did we miss? Leave your favorite Arrow episodes in the comments!