Dungeons 3

This is done in the "I Am Your Father!" level. This can be tricky or dead easy depending on how well you design your dungeon for invasions and how much you pay attention to invasions. If you create convoluted and winding paths for Heroes to traverse, linking up all dungeon entrances to a funnel point, make full use of the Demon Gate spell to respond to invasions and create lots of traps, you'll be fine. The Dungeonheart must not take a single point of damage for this trophy. If it stays at full health throughout the level till the point you activate the summon Ultimate Evil spell, you'll get the trophy.