I would use Jellicent over Regice because of Jelly's supremacy to all.
Jellicent has great special defense and HP and a great typing as well. With access to Will-O-Wisp, he can pseudo-boost his own Defense to boot. Three immunities to Fighting, Normal, and Water, and resistances to Fire and Ice are no joke either. Don't underestimate this jellyfish.
Jellicent also works with Leftovers providing recovery from Hail Damage.
Role: Special Wall
Trait: Water Absorb
EVs: 252 HP / 36 Def / 220 SpD
~ Toxic / Will-O-Wisp
~ Shadow Ball / Ice Beam