CONTAINS SPOILERS

Initially you'll come across bomb throwing sunflowers that will launch an explosive at your location. Fire at one from range and dodge as soon as it spits. Later, you'll acquire a new ability that lets you cast explosives with the Bomb Spell. This is obtainable once you reach the Mushroom Dungeon. Be careful, if you're too close to the detonation spot, you'll take damage from the spell.