So this game introduces a new monster "Form" - Bomb Monsters. They start with a countdown over their head, and if it reaches 0, they explode and damage everyone.
Here's the four types in this game:
And here's a "Bomb" type (which I killed in a turn and a half, so I don't know how big a threat they'll turn out to be later on):
iirc back then I played the japanese version.I encountered a "bomb" golem and can't killed it in time in time it cause around 800-1000 damage killing my entire squad in hard mode.