Jelly King is bored and commits suicide
This is not a bug I think but more like an exploit.
So here we are, me and my party, failing hard @jelly king. We are basically all dead and just chatting. Suddenly player "ilovetodance" notices the Jelly king's health bar is dropping and he is NOT being healed. How is this possible ? Apparently the exploding blocks damage him when they spawn and he is on top.
It took a while but after a couple minutes (half an hour?) the gelatinous foe was done for. He had committed suicide and we called it a draw.
http://imgur.com/2f1MyS6 <---------- Notice his health bar.
http://imgur.com/PvWYsly
http://imgur.com/pI3V0Cu
http://imgur.com/xDu6glg
http://imgur.com/eHFZEiG <--------------- Now it's almost depleted.
http://imgur.com/qGn6PXS
http://imgur.com/hnMqFZi <------------- He is dead, sadly we caught him off camera but you can see those "jell factories" are nothing but goo.
http://imgur.com/ctuVA71 <------------- Hello free token.

That is... actually really funny. I mean it still requires a spark so it's totally not worth it but it should probably be fixed anyway. Maybe just have him auto-heal a little bit?

This works on all monsters actually, even knights. Thing is that only a few monsters instantly break the blocks that spawn on them. When it happens to other monsters they take an unnoticeable amount of damage and are trapped by the block.
Hahaaaaaahhahahahahahhhhah! Im going ta try dat