Elder Spell: Swan Song

You attempt to wrest control of a spell from the creature casting it, turning the magical energy away from its intended use and towards the summoning of new life instead.

If the target is casting a spell of 3rd level or lower, its spell fails, and instead of the intended effect, the spell summons a beast of the spellcaster’s choice of a CR equal to or less than the level of the interrupted spell. The summoned creature is under the spellcaster’s control, acts at the end of its turn, and obeys any mental commands the spellcaster issues to it (no action required). 

The summoned creature is summoned for one minute or until concentration of one minute ends.

After a single use, this spell is forgotten.