crushing buttcheeks

you will your's or someone else's buttcheeks to grow 5 times in size. you can bounce on them, and they will allow you to float in water. you can also attempt to sit on someone. the target must make a dexterity saving throw. on a failure, the target takes 3d10 bludgeoning damage and is restrained. on a successful save, the target takes half as much damage and isn't restrained. at the start of each of your turns, the target takes 3d10 bludgeoning damage. at the start of each of the target's turns, it can make a DC 16 strength saving throw. on a success, the target is freed from the buttcheeks. while restrained, the target has disadvantage on all melee and ranged attacks it makes.