Dungeon Defenders

The Skin of Your Teeth Award is given for completing a level with the Crystal Core at less than 100 hitpoints left. Obviously you will need to purposely let some mobs reach your Crystal Core and damage it enough to that level, then finish them off. Each Crystal Core typically has 1500 hitpoints. Only one Core in the entire map needs to be at less than 100 hitpoints for the award to be given at the end of the level.

You can see if you have achieved the award at the end of the round by checking the Hero tab at the Crystal and pressing . You can also check it at the Crystal in the Tavern.