Tails' absolute refusal to give up throughout the entire lower city after being put through a meat grinder several times. It gets to the point where his body starts to try and cannibalize itself to heal his wounds. Talk about Heroic Resolve.
Tails' backstory establishes him as the closest to being a Badass Normal that the Sonic crew has.
Tails' duels with the duelists on Taris. Instead of going for the normal manner of fighting each one of them, Tails duels them one after the other with pretty much no break in between.
The duel with Bendak Starkiller in Chapter 043. It's built up over three chapters. Tails is healed up and restored from all his trauma in the Undercity. He gets a shiny new set of custom armor from Kebla Yurt. Tails and Bendak Starkiller go all out with shields, heavy blasters, vibroswords and grenades. Tails is at full power with his tail-blade and helicopter skills, slowly chipping away at Bendak's defenses, until he suddenly whips out a stolen lightsaber!! But Tails still wears him down until he can deliver the knockdown blow. The real kicker? It was NEVER Tails' intention to kill him! Tails engineered the entire fight to get Bendak arrested. This is a fight the game developers would only give you Dark Side points, but Tails managed to beat him the Light-Sided way.