Sacrifice: Weak. Just how much HP do creatures have, generally? Less than 10 sans a few exceptions. And Gravity Pull does the same thing - makes another creature take damage instead of you, so it's like you had that much more HP. Heck, it's better, as the overkill damage is lost.
Wings: Sounds alright as a spell.
Inferno: Up the cost and it's good. Nice concept.
Jellyfish: He said that. Arctic Squid does the same if not a better thing for a lower cost.
Midnight: Also a nice concept, and a stasis card, pretty much.
Planet: It's really overpowered, but I must say it opens piles of strategies. Aflatoxin yourself and play this and have an Otyugh out for the time, use other mobspammers... Idea is nice, but for those other games. Not for Elements.
Ghost: Also leads to some interesting strategies. Haunt heavy hitters, kill them, get them this way and then haunt more heavy hitters so if your originals die you still have them. I'd up the cost, the ability is pretty awesome.