I strongly recommend writing a MimicBot that goes through two iterations before allowing itself to exit with a fixed probability.

You can deal with those special cases that way. I was going to use a flatter, less quiny approach.

def special_casing_bot(opponent)
    if acts_like_cooperate_bot(opponent):
        return DEFECT
    elif act_like_other_exploitable_bot(opponent):
        return DEFECT
    elif special_case_3(opponent):
        return DEFECT
    elif special_case_4(opponent):
        return COOPERATE
    elif special_case_5(opponent):
        return DEFECT
    # etc
    else:
        return mimic_bot(opponent)