Rarity: 5★ to 6★
Despite the targeting change and boost in power, it's relatively meh. Y'shtola isn't really carrying CG Fina/Ayaka-levels of SPR to proc with its power to amazing levels of damage for finisher standards. What makes it worse is that Y'shtola has 0 SPR passives post-enhancements, so the damage is really lackluster. Plus, it's needlessly expensive on Gil and Crysts.
This is great, more defensive stats for the healer. Base potless MP going from 190 to 224, HP going from 3029 to 3634, and DEF going from 110 to 132. HP and DEF are awesome by itself, the MP boost combos well with the innate Auto-Refresh on it for a slightly better MP recovery.
Cleric Stance gets some amazing changes. One, it no longer cripples her healing ability, it instead boosts it. The level of the MAG/SPR self buffs are one of the strongest in the game. Two, it grants herself LB Fill rate and her maxed LB is amazing, 54% mitigation for one turn at the cost of 16 LB, with the buff and some LB equipment, it'll be spammable. Three, the turn extension, reducing the need to refresh it, which is nice.
These changes are awesome, while the ailment cleanse is niche at best, the MP recovery is where this enhancement shines. Zargabaath carries a similar ability and it's one of the reasons why he's good, same case here.
Y'shtola gets some nice enhancements but she isn't going to top the non-Ayaka/CG Fina/Tilith healers out there. None of her enhancements boosted her Raise or Curaga, so units like enhanced Garnet, Rem, and Roselia still beat her in terms of healing power, but she still has innate DC and a great mitigation LB going for her. Thanks to Cleric Stance and Benediction changes, she can flex as a decent support/healer, with her LB spam and MP recovery.
Overall, she can fill out the healer role very nicely for new players. While her MP recovery and her LB spammablility will come in handy for veterans.
Shroud of Saints, Cleric Stance, and Benediction are her priorities. You can ignore Holy, while Cleric Stance to Holy is a decent combo, the required setup for the finisher damage isn't really worth.
While the Ice resistance is niche, the HP boost is solid, especially when the unit getting it is a fully dedicated damage dealer.
Rarity: 4★ to 6★
So Master Thief gets both Treasure Hunter and Gil Farmer passives, making Xon an insane cryst and gil farming unit. If you're using Xon on your team, it's most likely that you're farming cryst/gil/item drops anyways, so you definitely want this.