Ayok's Timely Transmutation

Ayok the Trifling is a tiny blue Kobold wizard, and rarely beloved by those he met.  It became clear to him that he'd be in danger wherever he went.

This spell is contingent on the caster dropping to 0 hit points, and when this condition is met, the spell activates and the caster's dying body is changed similarly to a Polymorph spell into a beast chosen at the time of the casting.  The new form has its normal hit points, armor class and other statistics, and has a natural imperative to get to safety and understands who it's enemies are.  The Polymorph however only lasts for one minute, during which the caster can attempt to escape or hide or otherwise evade their assailant, using whatever locomotion is available to the beast form chosen.

If the beast form takes damage equal to or greater than the beast's hit points during the spell, the caster reverts to their natural state, still at 0 hit points but stable.  If however the beast form can evade damage for 1 minute, when the spell ends they revert to their natural form with 1 hit point plus their Intelligence modifier.