Morph Creeps

From CC Wiki

Morph Creeps are a creep type in DesktopTD. When they emerge, they pretend as Normal Creeps. However, they change their bodies into Dark Creeps as soon as they enter. After that, they change themselves into Immune Creeps and Fast Creeps in order. After that they will turn into Normal Creeps, to start the circulation again. Since they can morph into Dark, Immune and Fast creeps, they are harder to destroy than normal creeps. However, players do not need to worry about them if they're prepared for defending every type of creeps. That's because they are more fragile than ordinary Dark Creeps, their immunity to frost is limited and they're slower than the real Fast Creeps.