Piranha Plants are a classic Super Mario enemy, resembling a Venus Flytrap. In the original games, Piranha Plants normally lived inside pipes, but in Super Mario Maker they can be placed anywhere.
The basic Piranha Plant is simply a stationary enemy which cannot be stomped. In a pipe, it will emerge for a few seconds, then retract. It will remain in the pipe if Mario is far away, or if Mario is standing directly adjacent to or on top of the pipe.
In the Super Mario World style, Piranha Plants are replaced by Jumping Piranha Plants. These are slightly smaller, but jump straight out of pipes instead of emerging.
Shaking a Piranha Plant turns it into a Fire Piranha Plant. This periodically shoots small fireballs which fly at 45° or 22.5° angles, in whichever direction is closest to Mario. Unlike in the original Super Mario Bros. 3, the fireballs are stopped by solid blocks. When placed inside a pipe, a Fire Piranha Plant will breathe fire once each time it emerges.
When wings are added to either type of Piranha Plant, it periodically flies straight upward for several blocks, hovers for a few seconds, then descends. A winged Fire Piranha Plant breathes fire once per hop. A winged Piranha Plant placed inside a sideways or upside-down pipe will fly straight outward from the pipe instead of up.
Piranha Plants of all types can be made large with a Super Mushroom, but their behavior does not change.