The rollerball is “controlled” by one and running inside it, like it is a hamster wheel. The rollerball can be rolled fast enough that it can kill enemies by ramming into them. In addition, the user can jump while in the rollerball, even though it may not seem like that at first.
The rollerball is uncommon throughout the game. It appears a few times throughout the game, but never in secrets.
The rollerball can do a lot of damage if it rams into an enemy. Enemies as strong as the Albino Cyclops can be killed in one hit by ramming into it.
When using the rollerball as a weapon, try to strafe to the side while rolling towards an enemy. The rollerball's speed lets the player dodge attacks and running straight to the enemy will make the player take some damage during the trip, even though they'll kill it. Doing this a few times will cause the rollerball to take a good amount of damage.
The rollerball's speed can be quite useful for various things, such as avoiding enemies' projectiles, grabbing items that are needed, and for outright running past enemies.