I like how the final boss actually had mechanics, but it's stupid how your success is based off of Random Number Generation. You pray that you get the one where he doesn't teleport for 6 seconds most of the time and that you don't get the one where he summons a 3rd wave of monsters before you even finished the first wave's lava golem.
The last boss's attack that makes runes appear on the ground is ridiculous. It does a TON of damage, and you don't have a chance to dodge it, you just hope you don't happen to be on where he's casting it.