It’s either “Beautiful Realm” or “Call of the Beast,” and it’s the nymph ability to summon creatures that align with their element. For example; nereids can summon tentacle monsters or other beasts made of water, anthousai nymphs can create man-eating Venus flytraps, etc.. They almost always listen to the commands of their respective nymph. As long as the nymph controlling it isn’t harmed or killed, the beast will continue to rampage and eat their target.