Recently I started going through the Dungeon levels again, using the Jelly Cube in various combinations. This combo works on a surprising number of the Dungeon levels:

mana
jelly cube
bomb
skeleton

Notice: No shooters of any kind, no barricade, no living wall, etc. The only barrier is a mana crystal which is fairly fragile.

I find the jelly cube not only powerful when used correctly, but amusing to watch as it wiggles slowly from one place to another, often trapping heroes that are attacking it.