You pull yourself up another 15 feet or so. (new round). You now feel the full brunt of the necrotic rain (starting your turn in it/13-5=8 damage and slowed) and are again struck at by the tendrils that it seems to emit (15-5=10 damage and held under the rain). You are able to drag yourself up another 10 feet (with a move action). You are within 25 feet of the top, and can keep climbing..or?
Buckthorn: you solidly strike an eye. Nothing happens. Then you hit what may be a trapdoor over a mouth. It bounces off. Of course, if someone was down there with the righ skills (theivery...) they should be able to pop it open.