MimicBot cooperates with probability ε

You mean defects with probability ε.

No, I did not mean this, but I left out an important word: I should have said MimicBot cooperates unconditionally with probability ε.

MimicBot will almost perfectly mirror the strategy of its opponent. Most of the time (probability 1-ε), MimicBot returns the result of a simulation of its opponent against MimicBot. If you're fighting MimicBot, you should expect it to think and act almost exactly the way you think and act. If you decide to always cooperate with MimicBot, MimicBot will decide to cooperate with you. If you decide to always defect against MimicBot, MimicBot will (almost always) decide to defect against you. If you play a mixed strategy against MimicBot, MimicBot will play an almost identical mixed strategy against you.

The slight imperfection in the strategy mirror (cooperating unconditionally with probability ε) is necessary to avoid infinite recursion