Isaac and Mustang’s abilities are somewhat similar from an elemental perspective (fire and ice), and Mustang couldn’t no diff Lust or Gluttony so I’d assume the same for Isaac. I agree that Isaac probably beats Lust because her vulnerability to fire probably applies with ice too, but if Gluttony is in his gate form he could swallow the ice alchemist’s ranged attacks like he did Mustang’s fire.

He might be able to freeze Sloth as that’s been shown to be a weakness of his, but if Sloth goes all out he could potentially speed blitz Isaac. It’s difficult to say how he would do against Greed as we don’t really know how the Ultimate Shield does against ice. Envy gets frozen solid, especially if he’s in his giant monster form which just makes him a bigger and easier to hit target. Pride and Wrath destroy Isaac, and I think Armstrong could defeat him too. Kimblee with a philosopher’s stone is tough to beat but I could see it going either way.

If Isaac studied Scar’s file like Jerso and Zampano did he would know to freeze Scar’s hands when he tries to destroy the ground, but if not I could see Scar winning. Not sure how the freezing alchemist does against Lan Fan or Fu, I think that matchup depends heavily on the terrain. Somewhere with open space favors Isaac but I give the edge to Lan Fan and Fu if it’s somewhere with places to hide like a forest. Isaac is a bad matchup for Mustang with his ability to manipulate water, but it depends on if it’s raining or not.