When we first met Lieutenant Paul Stamets (Anthony Rapp) in episode 3 of Star Trek: Discovery, it was easy not to like him. Discovery's resident astromycologist and Chief Engineer was an arrogant and irascible academic who repeatedly butted heads with Captain Gabriel Lorca (Jason Isaacs) and Michael Burnham (Sonequa Martin-Green). Stamets was single-minded in his pursuit of his mission - unlocking the key to the USS Discovery being able to instantaneously travel via the Mycelial spore network - and not Lorca's mission, which is to win the war against the Klingons. Just three episodes later, Stamets is practically a new man. Suspiciously so. Is this the same Paul Stamets or has he been replaced with a duplicate from the Mirror Universe?
In episode 5 "Choose Your Pain", Stamets conducted eugenics experiments on himself. He injected himself with the DNA of the Tardigrade which was able to communicate with the Mycelial spores. As such, Stamets was able to take the place of the Tardigrade and communicate with the spores himself, allowing him to serve as navigator for the spore displacement drive. Rather than kill him, or do irreparable damage to his mind - Stamets' partner Dr. Hugh Culber (Wilson Crews) checked Stamets out and found him ship shape - Stamets seemed to have his mind expanded by contact with the Mycelial network, which he continued to do. Stamets has also seemingly undergone a personality change; he's now laid back, enthusiastic, and a lot more... fun. He even excitedly drops an F-bomb or two.
The final shot of "Choose Your Pain" showcased a creepy moment where Stamets stepped away from a mirror and his reflection remained, then moved by itself. This heralds the coming of the Mirror Universe, but maybe the Mirror Universe is already here. Did Stamets simply undergo some sort of psychic reawakening that altered his personality (for the better, or at least to be more entertaining), or did a duplicate of Stamets emerge from his first foray into the Mycelial network? It's possible Stamets just underwent a personality boost, but we were purposely shown creepy business with the mirror, so something involving the Mirror Universe is definitely up with Stamets.
Traditionally, Star Trek characters and their Mirror Universe opposites are different people who are identical but are independent of each other. Mirror duplicates are known to jump to 'our' universe and often recruit their opposites for a mission in the Mirror Universe. Discovery may be looking to rewrite the rules of the Mirror Universe (despite Star Trek: Enterprise, which takes place a century before Discovery, already venturing to the Mirror Universe) to keep fans guessing. It's possible in Discovery, Mirror opposites can now possess people in 'our' universe, perhaps through some means by way of the Mycelial highway. It could be that physically, this is the same Paul Stamets, but his mind is possessed by his Mirror opposite. This may explain his reflection; maybe 'our' Paul Stamets is trapped in the Mirror helpless.
Though Stamets' new upbeat personality is noticeable, his behavior hasn't rung any alarms from his crew mates or from Dr. Culber, who lives with him and knows him best. His crew mates even seem to be enjoying the new Stamets and since none of them seem to be aware of the Mirror Universe, they wouldn't automatically think he's been replaced with a duplicate. The lone exception could be Captain Lorca himself, who regards Stamets with more suspicion than the others. This could be because Lorca is simply more paranoid, or it could be because he himself might be from the Mirror Universe, as some fans have theorized. Whatever the truth to be revealed will be about Paul Stamets, it's bound to be effing cool.
Star Trek: Discovery streams Sundays @ 8:30pm ET on CBS All-Access, on Space in Canada, and internationally on Netflix.