A lifegain deck gets a ton of triggers from Bogwater Lumaret, plus it enables combos with cards like Warren Soultrader and Lisette, Dean of the Root that require lifegain to establish their loops
It allows you to build a deck full of creatures that would work better when mashed together into one giant creature
Absolute Virtue Choco, Seeker of Paradise Cid, Timeless Artificer Edgar, King of Figaro Emet-Selch, Unsundered Gogo, Master of Mimicry Golbez, Crystal Collector Hades, Sorcerer of Eld Hope Estheim Ignis Scientia Jill, Shiva's Dominant Kefka, Court Mage Kefka, Ruler of Ruin Locke Cole Matoya, Archon Elder Noctis, Prince of Lucis Omega, Heartless Evolution Quistis Trepe Sephiroth, Planet's Heir Shantotto, Tactician Magician Shiva, Warden of Ice Sin, Spira's Punishment Tellah, Great Sage The Emperor of Palamecia The Lord Master of Hell The Lunar Whale The Prima Vista The Wandering Minstrel The Water Crystal Tidus, Blitzball Star Ultimecia, Omnipotent Ultimecia, Temporal Threat Ultimecia, Time Sorceress Ultros, Obnoxious Octopus Vivi Ornitier Xande, Dark Mage Y'shtola Rhul
Nearly all the differences between the two games come down to DeNA's title being more forgiving
Its something that they look forward to