aha, the reason no one will play a two player game with me even to this day!
Yes many fond memories... level 28 of Mayhem still haunts me to this day. I took weeks of trying to complete that. One lemming to save, and about 9 minutes to do it in.
Two player lemmings is where I earned my reputation as an "utter utter bastard!", to the point that SWMBO (who was my beloved GF at the time of lemmings release) is highly wary of playing any two player (computer!) game with me these days. There they would all be, happily walking safely to the exit, green clad lemmings in one direction, blue the other. Could I resist the temptation to upset the happy balance? It seems not. Quick turn one around with a quick attempt to build by some obstacle, or area of confined headroom, and then "oops", there appears to be a blocker right in the middle of someone's carefully constructed bridge! Or, for devastating effect, (my speciality), dig the ground away from under the opposing exit and watch them frantically try to get a builder to repair the damage. Oh how easy it was to ruin it all with a basher when they finally managed.
I can still hear the exasperated screams of "oh, I am not playing with you any more!" ;-)))
Errata : SWMBO was just read this over my shoulder, and proclaimed "its not just me", "its the reason that nobody will play two player lemmings with you! In fact they are now wary of pretty much any multi-player game, right from Scrabble to Monopoly!"