Namely, the trio of uberness, in order of greatest to least unprecedented:
1) Miffyre--long story short, she's completely unprecedented. 1 SP on auto with no floating requirement on a unit out of range of returns and 40 damage SSs (even + sala)? And on top of that, is a huge ally against EN? She basically puts Marduk and Urgrant to shame. Also, when you stop to think about it, perhaps the biggest gap between units in this game is between level 3s and level 4s. Level 3s can be rushed out multiple turns in a row and can go down to SSs. Once you start getting into the realm of level 4s, the game was not balanced around rushing them out every turn the way Miffles does. And when you consider that the level 4s she pumps out aren't just sum of their parts, but Refess units, who are notorious for getting exponentially stronger, you can see why she can become such an issue.
And that's just on the SP-genning end. As bonuses, she gives EN the proverbial finger (though I don't suppose that's a new development, Refess has always had Lawtia's number), and I'm not sure how much she affects the serpent matchup, though I don't have sympathy for Falkow in Refess matchups.
2) Phoenix chick--at first it looks innocuous, until you realize that this thing is a max-HP hate immune field-wiping AoE tank that if you can't do 120 damage to it in one turn, look out. The biggest issue about this card though is that for a run-of-the-mill level 5, it's a game changer against any strategy depending on concentrated sources of large damage (bigs, other mids). And if you want to really humiliate someone, spam holy shield on it.
3) Verlaat--it's not so much that he's unprecedented (Bringer), as the fact that A) he's almost as good standalone B) has a better action C) is in the sphere with the best and most SP-generating options and D) has the best combo buff in the game bar none (BKR doesn't come close to 9 ticks regularly). It's just that the reason people see him as somewhat fair is that when he comes down, is he your worry or the SP-generating miffles suddenly swinging at you for 40+, the Judie dishing out 70+ damage on her own (90 once you factor in her buff), or the 35+ damage guardian with 25 defense?
So, let's propose some nerfs:
Start->auto. At least gives you a chance to get your utility units back if you kill her before she can move.
Stats: put them into worse early-game baskets, take from better early game basket. 55 HP->35 HP. Agi 1->2. Range 2->3.
SP generation auto: requires 1 SP, generates 2, instead of 0->1. At least gives you a chance to disrupt her with things like shades, nightwings, gafc SSs, etc...
Basically, it'll force the mid refess player to actually tuck her away securely instead of just dropping her in behind the refugee citizens and then rushing out units that should not be rushed out.
Close skill: lvl 6->lvl 7. Close skill conditional on max HP > 0 (I mean I understand why he gets his max HP reset, because he morphs from 30 to 90, but this is an oversight IMO). This should at least give an out for the few max HP-reducing techniques other spheres have (Nue, though not like EN needs the help, Cassie, Jack's trash action, Francis), as well as not make large single hits completely obsolete.
If that's not enough, make the action skill cost 2 SP as well. One-way 30 damage to your opponent's entire field for 1 SP? Um?
I'm not quite sure what to do about this guy. Possibly remove the 10 DF buff on open? Drop his atk by 10? Honestly he seems to be more a symptom of losing to mid refess than a cause.