When Sonic is fighting against a regular threat (Hard Boiled Heavies, Metal Sonic, etc.): Tails jumps in to help.
When Sonic is getting his ass kicked by an enemy he can’t hope to defeat (i.e. Infinite): Tails does nothing, panics like a baby, and when Sonic is down, cries like it’s his fault because it actually is his fault since he didn’t do anything.