3-3 Poisawan Inner Area: after Iluzija, Marco mutates into a Gnezdo; his explosives are left where it falls once you kill it.
Use
Blows open the locked gates in the room where Marco dies. After the scene you head downstairs.
Against the Gnezdo: scatter the swarm with the shotgun to expose the queen and empty the gun into her from mid range; only killing the queen ends it. There are 5 crates around.
