An angry Big Zen-chan, from Bubble Memories.
Anger (怒り Ikari?) is a recurring game mechanic in the Bubble Bobble series. It is a state taken on by enemies that typically results in them moving much more quickly, and in some titles, alters their behavior entirely. Enemies enter an angry state either by escaping from being trapped in a bubble or being otherwise incapacitated, or if the player takes too long in a single round and the "Hurry Up!!" indicator appears.
Some bosses may take on an angry state in certain titles if receiving enough damage.