Agents Of SHIELD: 10 Best Villains
9. Agent 33
Courtesy of Daniel Whitehall, SHIELD agent Kara Palamas was brainwashed early in the second season and turned into a weapon of HYDRA, complete with the nano mask that allowed her to assume the identity of others, which backfired when Melinda May's face was scarred onto her own.
After Whitehall's death, Agent 33 allied herself not with SHIELD, but with Ward, who "freed" her, giving her back her sense of self and helping to restore her own face, the two inevitably coming to love one another. Though she was eventually taken back into SHIELD custody, 33's permanent nano mask allowed her to escape and kidnap Bobbi Morse, her and Ward luring the team into a trap as revenge for all she had gone through.
Because Melinda May is awesome, she turned the tables on the duo, tricking Ward into killing 33, an act that finally put the conflicted antagonist out of her misery but served to fan the flames of Ward's hatred for his former allies headed into the third season.