In "Above and Beyond," there is a Prismarine Colossus near to the portal in Terminal Space.
After Romeo notices Jesse's trespass, he summons four Prismarine Colossus. The Colossus vanish after the Golden Gauntlet bursts a shock wave.
After Romeo's powers get stripped off, one of the remaining Prismarine Colossus becomes glitched, goes berserk, and breaks the bridge to the exit portal. If Jesse chose to save Fred's people in Episode 4, it is distracted and killed by the Giant Enderman.
Romeo mentions that Prismarine Colossi require Admin power to control. Therefore, the reason that the other Prismarine Colossi in the sea temple stay neutral is possibly because they are all under Romeo's control, despite their hostile nature.
The Prismarine Colossus controlled by Romeo in "Giant Consequences" drops Prismarine Shards on death, but the Prismarine Colossi summoned by Romeo in "Above and Beyond" drop nothing when destroyed.
The Glitched Colossus may be glitched because of Romeo being glitched.
The Prismarine Colossus and the Prismarine Soldiers share one weakness: the back of the head(s).
Romeo's Prismarine Colossus, which is directly controled by Romeo.
The glitched Prismarine Colossus in Terminal Space.
Romeo's Colossus in Giant Consequences.
Romeo's Colossus in the Sea Temple.
Glitched colossus death (determined)
A Prismarine Colossus seen near portal of the Terminal Space.
Romeo's Collosus in "Giant Consequences" holding a Clock.