Killer Cat (殺意のネコ Satsui no Neko, Murderous Cat) is an event enemy appearing in the Day of the Cat Event. Completing any stage in this event will unlock this enemy's cat counterpart, Killer Cat (Rare Cat).
This is basically a heavily watered-down Crazed Cat with a Black attribute, but it gains a strength magnification as the player progress through the event. Luckily, it only attacks one cat at a time (single target), but spawns in huge groups in the last stage. To beat them, you can outlast them as their spawn rates eventually decrease to a manageable level.