Finish survival mode without paying attention to the game.
Once the Tesla power is maxed out, if you can get Tesla gun, while you hold down left click, right click in the middle of the mushroom patch and you'll lock the cursor to auto-fire. The Tesla gun will take care of the rest. Sit back and grab a beer and watch those animals fry! Or go away and do something productive :)
Trial 4, if you are using the Undead Knight (haven't tried with other heroes) you can beat the Beast with a little micro-ing. The Beast doesn't do that much damage to you if you are right up against him, so first send out some heavy hitters (White Tiger, Black Dragon work really well - high damage and health, and also reinforce quickly) to whittle away some HP, then then the Beast gets to your Hero, have him charge so that he's always up against the Beast. This will also push the Beast back and allow some of your other units to damage him. Just make sure to use the Undead Knight's self healing when he gets almost half HP.
Is there a bug where you don't get the Iron Fortress after beating the Goblin Rangers in Trial 2? I beat the trial twice, but I don't get the achievement to get the Iron Fortress :(
 "Theme Hotel"){kind=icon}
 "Mushroom Madness 3"){kind=icon}
 "Bunny Invasion 2"){kind=icon}
 "Relive Your Life"){kind=icon}
 "Epic War 5"){kind=icon}
 "Tyrant"){kind=icon}