Nature will rise against you

This is one of the tankiest builds in the format in my opinion.

Malfurion - Liferoot staff can heal the party up to 18 per turn PASSIVELY if everyone is using nature abilities. This is the key to this comp. Additionally, he can root, AoE heal, AoE damage or speed up the whole party. He is definitely the number 1 in nature comps.

Guff - In this team, he is a better tank than any protector. Ironbark gives him taunt and a ton of stats. He also has an ability that buffs the whole party including the bench, which is important for the next guy.

Brightwing - The bench-swapping is a very unique ability. Im not sure how good it is in PVP, but in PVE it will be very useful to keep your party healthy.

Bru'kan - Buffing the damage of the whole party and he can also slow an opponent by a lot with Muddy Footing.

Lady Anacondra - Serpent's bite gains double bonus from +nature damage and she is also a great healer.

Morgl - If you want to be consistent with healing and using nature abilities, he is your best 6th in slot merc. If you are concerned more about role balance, you might try someone else like Thrall instead.