Curse of Bonelessness

You touch one Large or smaller creature that has two or more legs it can use for locomotion. The creature must make a successful Constitution saving throw or its skeleton (or exoskeleton) turns to soft cartilage that cannot support the creature's weight or movement. The creature falls prone and is incapacitated for the duration. Whenever the creature takes damage while under the spell's effect, it may make another constitution saving throw, ending incapacitated on a success.