I didnt get iron man, but kept playing and got all the achievements (except hard, not losing life on survival, and not getting hit, because i did not attempt). After beating the game, tried prolouge again, and got iron man. Maybe it has something to do with getting 6 on the chain when the carts shoot at you.....i didnt get 6 chain when i didnt get achievement, but when i did get 6 chain, iron man unlocked. Dont know if this is just coincidence or what...?
need a boosting partner for: