Since the blue keeper in hero cove is stupid and mindless
(as in he does not make lairs and hatcheries for his monsters)
here is a small but STRONG hint
drop an imp in his unclaimed land (use feel the power cheat or imp dies too fast)
possess it and make it dig through rock to the outside
then make the imp run to the hero spot and activate the alarm trap
this causes heroes like giants, a dwarf, and wizards to come through
run like the wind to stay out of their sight
stop possession of the imp and drop it at your dungeon heart
and watch as all the heroes walk into his dungeon and kill him
it takes a minute or 2 for them to beat him
but it sure is fun to watch as imps get smashed and arches get whacked
+ after activating the alarm trap you can look to see that it looks like its still going off