Terra feels like yet another "do you have healing" test (which at this point EVERYONE DOES since Deus among others just tested that EDIT: except Jowy/Tengaar) although I might be underselling her outlasting powers with that durability. Still trying to get a feel for that match but it feels like yet another one where the Heavies are just going to sweep. Give them better challenges!
Anyway:
Varkas and Sydonia (Suikoden) LOSS vs Oswin (Fire Emblem: The Blazing Sword): To save myself headaches I'll assume unites are that class of attack that can neither double nor be countered. Anyway, if Oswin can 2HKO Sydonia, he only has to survive two unites, followed by Varkas beating on him like... two more times. He might well do that, I'm not really sure. But... the issue is that Sydonia may evade. He's got 25% raw, and Oswin has 7% below average hit so we'll call that 32%. There's a decent chance that misses once. Oswin can improve his odds by using more accurate weapons, though... a Silver Lance + Slim Lance does 84% to average, which still kills Sydonia easily enough (0.77 pdur). So never mind that. Ugh. Can Oswin deal with ~3 PCHP physical damage? Eh... sure, I think so. If you scale him against Limstella-level attack he's 3.22, which seems reasonable enough to me. Good fight!