Ame vs PoB

Short answer is that PoB wins.

Long answer: I went back and forth a few times on this honestly.

The most important points to me were

1. Can Natsu hit MM?
2. Who's stronger (both sides argued that the other would struggle to damage their character)
3. Natsu heat vs tele-regen?

Can Natsu hit MM?

Yeah, eventually. Natsu is argued to have a large AoE, PoB does a good job as presenting the MM as (relatively) weak to heat and has a speed boost on top. Ame defends the points well, but he's aware of why the MM are in tier, so he's forced to argue things like Natsu having windup to his blasts, and the MM's regen. I think PoB did a better job overall.

Who's stronger/more durable/mogs

PoB earned several points for preempting Ame's arguments about piercing, and then dissecting the actual feats used to argue it in the second round (jagged cut, not in character yadayadayada). Ame does well supporting MM strength and durability, especially with his Superman scaling. PoB effectively counters by pointing out that Superman is less hurt by the MM than he is by In_Tier_Striking from Imperiex.

Heat vs Teleportation/Regen

PoB argues that Natsu's heat is higher than what the MM can take (lava kills), Ame argues that it's hotter, there's more of it so heat transfers and also MM can just leave and regen if they take damage. I lean towards PoB who rightfully pointed out various weaknesses the MM have, (heat vision does damage and it's not provably hot, lava literally kills it, ) and did an alright job defending Natsu's own heat.

My conclusion is that Natsu is stronger, probably struggles to hit the MM, but eventually will, either through AOE heat, the MM trying to grapple, or landing direct strikes, and then wins.