Dire Mutation

You scramble the genetics of a Large or smaller beast (or a summoned creature that has the shape of a beast) within range, transforming it into a hulking abomination. An unwilling beast must succeed on a Constitution saving throw to resist this spell. This spell has no effect on shape-changers or other creatures which are transformed by a spell or other magical effect. On a failed save, the beast becomes a monstrosity and its statistics change in the following ways:
• The target’s current and maximum hit points increase by 40.
• The target’s Armor Class increases by 2.
• The target's size doubles in all dimensions, and its weight is multiplied by eight. This growth increases its size by one category.
• The target gains the Multi-attack trait, allowing it to make two melee weapon attacks. If the target already has this trait, it can attack one additional time on its turn.
• The target’s attacks can use your spell attack bonus to hit, if it would be higher than their normal attack bonus.
• The target is hostile to you and your companions, unless it is a creature summoned by you.
The spell ends and the target reverts to its normal form if it drops to 0 hit points. When the spell ends, the creature’s statistics return to normal and its hit points return to the number it had before being transformed.

***From Dark Matters***