The Animal Shapes spell allows the caster to transform “willing” creatures in range into an animal.
The transformation lasts for the Duration for each target, or until the target drops to 0 Hit Points or dies.
Would an affected creature be able to drop this form at will?
On one hand, the spell explicitly states only 2 events can break it (spell naturally ending, creature dropping to 0HP)
However, it could be argued the creature no longer meets the criteria to be transformed since they are no longer willing.
The spell requires concentration which also lends credibility to the idea that the willingness check may be a continuous thing.