On the second boss, we were able to get out of bounds during the fight. Somehow the wall in the upper right corner of the room you start in could be walked through, despite visually still being there.
There's a section in Temple 2 where you can walk out on the blackness. It's a 4 square vertical strip roughly in the middle. You enter from the bottom left side. Again, doesn't break anything, but odd that you can do it. Sorry no screenshot, I can't seem to get my computer to capture/save anything.
Temple 3's Teleporter didn't give us a return option. The bottom left rune didn't show up on the circle when we returned to the surface. This was a hard online game with infinite lives, wizard/warlock duo. A few other teleporters were also not active (by choice or missing them). I'll look into which other ones we didn't turn on if that would help.
Here's some enemy feedback now that I've spent more time with the campaign:
BOSS 1 - They all wanders off way too much. I don't think it would hurt if they were a tad more aggressive to give more chances to actually land a hit, particularly for melee heavy characters. Even having them stay out a half second longer would be a much appreciated change to the encounter. All in all, the most frustrating part is still waiting for it to come back, only to get one chance to attack and have it wander off... again.
BOSS 2 - The blast radius on his far around him orb circle is freakin' huge! (at least on hard difficulty). It's almost impossible to approach him without getting hit by it at least once. A slightly longer wind up time before it has a hurt box or a smaller blast zone would make that attack not feel like it needs pixel perfect timing to avoid.
Also, do the icicles need to be there? It's tricky enough trying to dodge all the tracking projectiles to get a shot at the boss. Throw in frequent instant kill gigantic AoE adds an element of randomness that sometimes slowed the fight to a crawl. It would be nice if they were less frequent and/or smaller in size, like the dragon's meteor strike.
BOSS 3 - Holy crap, this guy on hard difficulty, holy crap. Is it actually possible for a player to solo him on hard? With just two of us we couldn't cope with the sheer number of enemies and attacks going on. He had healed himself back up to almost 50% because we were dying so often. No suggestions here, just felt the need to comment. Talk about a daunting encounter!
FIRE/ICE ORB WIZARDS - The hit box for their attacks seem to show up instantly with no indicator other then your own sense of timing, similar to the Boss 2 orbs. A few more frames of visible start up before they deal damage would make these guys feel far less cheap. Difficulty doesn't seem to make a difference for these attacks.
PLANTS/PINK HAT ENEMIES - They both do an out of the ground below the player attack. The wizard really struggles against these because he must stop moving to us any attack. I suppose this is more a wizard issue then the enemies themselves, but I still felt it was worth noting.
MINI-BOSS MUMMIES - If these guys are designed to be enemies you need to bait into traps to kill safely, job well done! If there is a way to actually melee them without being eaten alive by locust, it wouldn't hurt to offer a tip about it in game in a hard to miss spot.
SUN BEAMS - could you maybe open up the hallways these pass through so travelling past them isn't a chore in very careful button tapping to get a wall hug going? It hampers exploration and really turns into more of a frustration then a fun mechanic.
Overall it's a solid campaign. The difficulty has been frustrating in the good way. It makes me want to play smarter and try new strategies. Definitely feels like it was made with multiplayer in mind, as playing solo is actually pretty daunting! This is all meant as feedback, and is completely subject to opinion, at least for the enemy suggestions. The bugs are... well, bugs. XD