In Sonic Advance 2's Sound Test, the invincibility theme is named "UNRIVAL". What.
I think it's supposed to be short for "UNRIVALED." As in, having the invulnerability gives you unrivaled strength compared to the basic enemies, or something...
It also fits with the naming convention for previous invincibility tracks that had proper titles. The invincibility tune in Knuckles Chaotix was named Surging Power and in Sonic Adventure and Sonic Adventure 2 it was called (Still) Invincible...No Fear. Unrival fits right in with those.
Sonic Advance 2: How come that Dimps downgraded the graphics during the development? Just compare these screens:
The character's afterimage effect is transparent in early screens◊, but opaque in the final game◊, using the primitive "flickering sprites" effect for pseudo-transparency instead.
How did the characters survive falling from space to the Earth in the endings of Sonic Advance 2!? Every other game that had the "fall from space" ending hand them get rescued by someone in the Tornado, but not this one.