Fire button activates secondary ability (costs rings)

Sonic - Super Spin Jump (10 rings)
If used on the ground, Sonic leaps high into the air.
If used in the air, Sonic strikes the ground before bouncing back upward.
One second cooldown between usages.

Tails - Buzz Sentry (10 rings + 1 ring per second)
Deploys a flying robot that follows and assists the player.
If fire button is pressed again, robot will become dangerous to touch and strike the nearest valid target.
Deploy time is ~1.5 seconds. Additional arm time is ~0.6 seconds when striking.
Can be destroyed by normal attacks from enemy players.
If robot is too far away for too long, it will temporarily noclip through walls until it reaches its owner.
2 second cooldown between attacks.

Knuckles - Dig (10 rings + 1 ring per second while stationary / 2 rings per second while moving)
If grounded or clung to a wall, Knuckles will burrow into the surface he is attached to.
Knuckles is impervious to damage while burrowed, but can still drown or succumb to death pits.
Height is reduced while burrowed.
Knuckles will automatically exit from burrowed state if he leaves the surface or runs out of rings.
Pressing the jump or fire buttons will launch him from his burrowed state, sending damaging debris in all directions.

Metal Sonic - Energy Blast (~10 rings per second + 5 on release)
Holding the fire button will charge a projectile burst of energy blasts.
Metal cannot be damaged while in this state.
Rings are rapidly depleted while holding fire.
On release, fires projectiles z-aimed at the nearest target to cursor. Projectile spread and amount increases with time held.
Shot will be canceled if Metal does not have enough rings on release.
Four second cooldown after releasing blast.

Amy - Wildcard (20 rings)
Random effect for eight seconds when activated. Player cannot use abilities while wildcard is in effect.
1) Player turns invisible and is intangible to all objects.
2) Player's gravity is flipped. Jump height is doubled.
3) Player is enlarged and impervious to all attacks. Will damage other players on touch. Speed, jump and gravity are reduced to 40%.
4) Player is shrunk and vulnerable to enemy player touch. Speed, jump and gravity are increased to 250%.
Twelve second cooldown after effect has worn off.

Fang - Bomb (10 rings)
Player tosses a bomb.
Does not explode on landing. Instead, it has a fuse of 4 seconds and will bounce off of surfaces.
1.5 second cooldown after each toss.