Agents of S.H.I.E.L.D.'s landmark episode 100 will welcome the return of Hive and Lash, two key characters from season 3. Hive was the immortal alien that inhabited the body of Brett Dalton's Ward while Lash was the Inhuman monster that hunted other Inhumans. Both Hive and Lash were killed, which suggests that both characters may appear in flashbacks.
Inhumans were a major part of Agents of S.H.I.E.L.D. during the show's third season. Melinda's ex-husband, Andrew (Blair Underwood) was a psychiatrist hired by S.H.I.E.L.D. to treat Inhumans. What Coulson and his team didn't know was that Andrew was actually Lash, a vicious monster that killed Inhumans. Andrew tried to redeem himself, but was eventually transformed into Lash permanently before being killed in a battle with Hive. Hive was the evil, parasitic creature that laid the foundation for HYDRA. After following Fitz and Coulson off an alien planet, Hive tried to infect the whole world, but was defeated in the season 3 finale.
EW reports that both Lash and Hive will be appearing in Agents of S.H.I.E.L.D.'s 100th episode, titled "The Real Deal". However, It may not be necessary for Blair Underwood to return, since his Lash form was played by Matthew Willig. As for Hive, there's no way of knowing which actor will play the character since Hive can infect and inhabit any dead body.
Season 3, the same season in which both characters appeared, was revisited in a poster for the 100th episode. It's possible that the episode will be a celebration of everything that's come before it by incorporating characters and moments from previous seasons. It's not clear if Agents of S.H.I.E.L.D. will accomplish this through time travel, flashbacks, or some other plot device.
With all the hype surrounding it, the bar has already been set high for the 100th episode. The episode is said to contain a "significant event" that will "destroy" fans, which suggests that the death of a major character could be in the cards. Fans are speculating that this "significant event" could have something to do with Coulson's deal with Ghost Rider, which happened in the season 4 finale. We know that the details of that deal will finally be revealed during the episode, and that it will impact every member of the team.
Agents of S.H.I.E.L.D. continues with "All the Comforts of Home" on Friday, March 2 at 9pm ET on ABC.