Sonic the Hedgehog 3 & Knuckles/Bugs

Level bugs

Move during end of level score tally

If a player times it right and jumps into Tails hands as he is flying at the end of the level the player will still be able to move during the score tally.

• 

  Sonic can move during the score tally

Not fixed in any version

Flying Battery boss (Hang Mobile)

While playing as Knuckles, in Flying Battery Zone act 2, the boss is Robotnik instead of Egg Robo.

This is likely due to the fact that the battle's perspective is different--the Eggpod and thus its pilot face the screen head on, and so require new sprites, which the artists did not implement for EggRobo.

• 

  Knuckles fighting Robotnik in Flying Battery Zone

Not fixed in any version (The hack Sonic 3 Complete by Tiddles addressed this by implementing sprites from an ending scene.

Mushroom Hill boss (Jet Mobile)

The same thing sometimes happens in Mushroom Hill Zone act 2, though not always. It happens more often after the player dies.

• 

  Knuckles fighting Robotnik in Mushroom Hill Zone

Not fixed in any version (again, addressed in Sonic 3 Complete)

Knuckles in Carnival Night

While playing as Knuckles, one can take Sonic's path in Carnival Night 2, then glide over the boss area revealing a load of junk.

Not fixed in any version

Knuckles Palette

Due to palette limitations, Knuckles' socks change colors; when you are playing as Knuckles, they are green. When you are playing as Sonic, Tails, or Sonic and Tails, they are yellow. Furthermore, as can be noted by entering Sky Sanctuary Zone act 1 as Knuckles through cheating, the two 'versions' of Knuckles have slightly different hues.

Not fixed in any version

Standing on LBZ spinning floors

If the player comes to a natural stop on the spinning floors after being rolled up into a ball, he will be using his standing sprite instead of the rotating sprites.

• 

  Sonic and Tails standing still on the rotating platform

Not fixed in any version

Triggering the LBZ booster infinite times

If the player does a spin dash in the right place and at the right time he will trigger the booster infinite times as long as he'll maintain his spin dash position.

• 

  Sonic triggering the booster while spindashing

Not fixed in any version

Corkey Doesn't Harm Knuckles When He Climbs

If Knuckles is climbing on a wall, Corkey's laser doesn't harm him.

• 

  Knuckles magically surviving Corkey's attack

Not fixed in any version

Hovering Knuckles in Hydrocity

If you climb in Hydrocity Zone below one of those up and down moving rotating blocks, it will push you down without resetting you to normal status when you leave the wall, resulting you are climbing in the middle of nowhere. This video might explain it a little bit better.

• 

  Just climb below one of those up and down moving thingies and get pushed down

Not fixed in any version

With Hyper Sonic...

Hyper Sonic's extraordinary abilities help to bring even more bugs and glitches into Sonic 3 & Knuckles. In particular, his double jump which allows him to boost towards any of the 8 main directions can bring quite a lot of confusion to the mix.

Mushroom Hill boss

By double jumping before the screen gets locked vertically, Hyper Sonic messes up the level scrolling. The level is still completable, though.

• 

  Note to self: do not jump this high

Not fixed in any version

Flying Battery

Hyper Sonic's ability to cross small walls and barriers with a double jump allows him to escape from the force field in the pre-boss in Flying Battery 2. By doing this you can go almost all of the way up to the second battle with Robotnik. However, the cloud and object sprites are corrupted until Robotnik runs away as part of the first battle.

• 

  Hey Robotnik, where are you looking?

Not fixed in any version

Mushroom Hill miniboss

If MHZ's miniboss is defeated too quickly (e.g. while it is still moving before it could arrive to the right limit of the screen), the Act 1 to Act 2 transition doesn't take place properly, leaving Sonic helplessly stuck at the beginning of Act 2. In order to hit the miniboss 6 times so quickly, Hyper Sonic's double jump must be used.

• 

  The score tally already doesn't look so good

• 

  Hmmm, last time I checked there used to be a slope there

• 

  Good, Knuckles won't come to perform the cutscene. Gotta wait 9 minutes and 59 seconds...

Not fixed in any version