Tree of Life

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Heitir Yggdrasill

You transform a willing creature into a small tree. While in this form, they are petrified, but their AC cannot be reduced below 16, their HP cannot be reduced below 1, and they regain hit points equal to 2d8 plus your spellcasting modifier for every round concentration is maintained. 

A creature petrified in this way can continue to concentrate on spells, but must still make concentration checks when taking damage. 

The creature reverts back to its original form when the spell ends.