2. Skarmory and Ferrothorn hate being burned by Will-o-Wisp or Scald and are both neutral to Ice Beam. Other Hidden Power Types could be considered because of this.
3. Pain Split is an Offensive-Recovery Move without being an actual offensive Move. Pain Split does rely on your HP being below your opponent's for maximum efficacy, yes, but you'll often be taking damage because Jellicent is a bulky Water and that's its job - damage soaking.
Why waste time restoring your HP with a redundant-coverage-and-somewhat-blockable Giga Drain or by using a Recover and not dishing out passive damage? Pain Split is crippling to a fragile opponent if you are at critical HP levels and you balance it with your opponent's (hopefully full) HP. Then you can potentially revenge-KO them if they cannot keep up their damage output with your bulk. Skarmory, Blissey, Chans-Eviolite, most defensive-style Water Types, and Ferrothorn aren't that bulky with a huge chunk o' health stolen, either. I'm not sure of interaction with Liquid Ooze, but it does make you recover while dishing out damage without relying on Grass Type's mostly-redundant coverage.