Bibi Grass, a plant-based pet...
All plant-based pets have one common characteristic: they do not like to move or make noise, which makes them rather limited in their abilities.
One of the most famous examples is the Venus Flytrap, which has the chance to instantly kill a monster of equal or lower level once a day, ignoring its defenses. However, this instant kill ability does have its restrictions. Bosses and certain special elite monsters naturally cannot be killed instantly.
Leo once used a Venus Flytrap pet to deal with a thick-blooded monster blocking his path.
Whenever he thinks about that monster's health, Leo gets a headache. The health of normal monsters is usually visible, but that monster's health was invisible. Leo had initially fought it for an entire day without killing it, and finally thought of using the flytrap's ability to get past it.