This is disgustingly unbalanced, although I do like a unit that can be paid with nexus health, just not a 7 cost one with stats this huge. Mundo shurima can reliably play mundo turn 1 of the game, playing 3 mundo, 3 calling, and a fair few 1 drops given his levelup wants a wide board to heal a lot.

On turn 1, you will almost always have a mundo on board, which is already way overpowered given the only downside is taking nexus damage, which you want to do to level mundo. Even if mundo dies the turn after to like a get exited or a mystic shot and go hard, you are never mad at that because your deck very reliably draws into mundo and the next one you play will level him on the spot, at which point you have a turn 2 or 3 attack for 8 damage with a fearsome unit with 4 health.

The most ridiculous thing however is the highroll.

Your opening hand contains either 2 munods ideally, or mundo, a rite of calling, and fireth or dunekeeper. You play mundo, your 1 drop, then rite your ephemeral 1 drop, either fireth or dunekeepers sand soldier, and play 2nd mundo. You have 6 nexus health, but will heal to at least 8 on this attack whilst dealing 16 fearsome damage turn 1 and still either having a dunekeeper or having an equipment in hand from fireth.

There is no deck in the game that can deal with this, especially since you are in PnZ and your opponent is on 4 health turn 1. You could just run this shell with a few more early units, a little draw, and a ton of burn and win a decent amount of games turn 3 without your opponent being able to do anything to stop it, especially with Porto canon healing you 2 and dealing 2 elusive damage when they attack.