Tank Push

A sliding-block puzzle wearing a battlefield. You are a frog in a small green tank, and the blocks you shove around are marked with letters that have to end up on the gates wearing the same letter. Push only — nothing can be pulled — so the first move of a level is usually the one that decides whether it can be finished at all. Tank Push looks like an action game for about four seconds, then settles into the oldest puzzle rule there is and gets steadily meaner about it.