>>96538972019, Kinsano Cyclops Raid but it was just a few infection forms. For an actual Flood figure it'd probably be the Flood-infected Cyclops from 2015, though there was also one in Delta series blindbags in 2016.
2014's Flood Invasion was far and away the best - you got two combat forms (one active camo), a carrier form, two tank forms, a whole pile of infection forms and even a piece of Flood material to "infect" the Ghost in the set. Was hoping they'd follow up with pure and ranged forms, no such luck yet though.