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.