Sonic the Hedgehog and Marsha also first meet in "Adventure Time 6: Creepy Fears". They both start rivaling each other due to both having superspeed. Even if once they get past that fact, they still have many differences. This doesn't result them in having much fights, but it brings out Marsha's anger.
Sonic sometimes teases Marsha for messing things up, calling even "Knuckle-head" at times, just like Knuckles. This rivarly hasn't disapeared quite yet. But overall, they can be great team mates and Marsha is also one of Sonic's best friends.