3 stars- all treasure must be in the treasure room at the end. treasure can be carried out by heroes and later returned by rats.
1 star- at least 1 treasure pile left in the level after all the heroes are gone. you only need 1 star to pass the level, and can replay it later with whatever new defenses you've unlocked.
sometimes it's useful to force waves early.
heroes normally will not attack a barricade and instead look for another way around. Only attacking it if they can find no other way.
some heroes (archer, wizard) will attack living walls on sight, others will just look for a way around.
thieves will stop disarming if they take dmg (even slime trails)
you can bait epics power attack, getting them to waste it on something cheap like a skeleton.
Once a hero is attacking something, it will ignore everything else. perfect time to drop a skeleton behind them.
if a hero sees an empty treasure room they will just leave the level, even if some treasure was dropped somewhere else in the level they haven't seen.
thieves are attracted to mimics. wizards-mana crystals. soldiers-tentacle garden. clerics will walk by defenses if they can. soldiers will stop to attack defenses.
mana crystals can be used as an emergency blocker.
defenses work out much better when used in combination with other defenses (ex: catapult behind barricade).
try to cover traps only thieves can disarm, to prevent them disarming them. even just dropping a bomb or skele in time will work.
since wall blades/wall pounder are invincible, put them in front of traps only thieves can disarm (ex: floor spikes). The wall blades will interrupt their disarming.
some defenses are powered up by lava vents. mana crystals, dragons, lava lobbers. Some others just get burned up. lava vents will ignite sticky tar.
if a jelly cube is destroyed before digesting the hero, the hero escapes alive. not so with a mimic.
jelly cube digests every hero in the square, and not taking extra time to do so.
heroes confused by looker can walk into (and be trapped in) jelly cube.
baby dragon can push heroes into jelly cube.
set a false wall to get heroes to backtrack through a gauntlet of traps they just walked through.
if a slime dies while still fresh he explodes leaving a 3x3 area of slime. his pathing prefers to not cross already slimed tiles.
baby dragon is good for pushing heroes back into traps and jelly cubes.
sticky tar can be ignited to cause dmg to a wide area of heroes. bomb, lava lobber, etc.
some defenses are flammable.
lava lobber, bomb, and wall pounder (more?) attacks stuns briefly.
if you time it right, you can hit a hero with a rock drop twice (baby dragon pushback).
There are walkthroughs for some levels on youtube.
There is a hidden unlockable defense. Here is the hint:
and the solution: