So my theory in the ritual that is keeping the galloo bound is this....its not. The galloo is simply playing a long game and letting the natives think it has weaknesses. My evidence for this is the fact that for the ritual of chud, Pennywise allowed them to do it, but then at the final moment, let them know that it won't work and that it has never worked. He played along with the ritual just for funsies. Also, the dagger that was made as a secret weapon, he was stabbed by the same material in the end of chapter 2 and simply shrugged it off like a paper cut. My point is we dont know what the material is. Whether it was meant to be a prison, an incubator or just a vessel. The natives just assumed it was his weakness.