From the Super Mario Wiki
The Flaming Tender is a spicy red pepper with an angry expression. Upon using the item, the user will begin to breathe fire, which they sweep back and forth. Any opponents that get close to the user will get hit by the flame and be brought to a complete stop.
In Mario Kart Arcade GP DX, the function of the Flaming Tender has changed, due to it being usable by all racers in this game. Upon being used, the Flaming Tender will temporarily set the user's kart ablaze, causing them to deal damage to any rival karts they come into contact with.
In Mario Kart Arcade GP, a variant of the Flaming Tender known as the Flaming Tender+ can be unlocked. This variant increases the duration of the attack.