Sasarai does about ~0.909 PCHP to average, if I am doing this right... (Sasarai's damage expressed as a percentage against the killpoint in the stat topic)
Lyon needs to at least take magic as almost average to make that really matter, since she can get 0.92 HP if I understand this correctly? Her... Mdef is 189 against a 220 average without skills, 229 WITH skills. Can she boost her Mdef by ~40 with skills while also keeping her HP buffed up?
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What are the "bunch of hax", Dark Holy Elf? I'm personally having a tough time seeing Lyon live through Land of Eternity, but my Sasarai respect is skyhigh, so...
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Going entirely from the stat topic, and I may be wrong here because the DL maths aren't entirely clear to me sooooo I'm just winging it with the numbers, taking defensive stat potency as valuing equally much in all games...
But Sasarai has 0.877 (0.88) HP taken against the averages without Luc/Yuber/Sarah. Otherwise that is 0.89.
His defense is 0.964 taken against the first average, 0.976 against the second. So he's just barely not average defense. Now, I don't know how potent S3 defense is, but he can get 242 against a 251 or 248 average.
Lyon on the other hand has 0.92 HP when being generous and holding her against a non-skill-influenced HP average. However, if I do that, I will discard any skill-influenced stats for her, so her Mdef is 0.823. She innately rejects earth with 6.4% proficiency.
Now, Sasarai damage is 0.909, as opposed to Lyon's 0.413 physicals.
Sasarai's damage seems to still be 1.00 PCHP against Lyon's godly Mdef+Earth defense. That is, using the method:
0.909 x 0.936, then that result x 1.177. It yields ~1.00 PCHP damage against Lyon, so there's really no way I see her as knocking that down to 0.91 or lower without skills available to her.
Lyon on the other hand does 0.413 x 1.036 damage against the average Sasarai doesn't like, which amplifies her damage to 0.428. That means she'll do around ~0.85 PCHP against Sasarai in two rounds? So she misses the 2HKO, if only barely.
Even MAG won't save her against a second LoE.
//EDIT: I think her phydmg is also amplified by the All-out Strike skill. If you let her skilltwink to survive a single Land of Eternity, arguably her damage falls enough to definitely make her 3HKO Sasarai... I forget what All-out Strike does completely, though! It's been a while.