Flaming Forest

The first area in Pikmin: Dark Forces and is where the Red Pikmin are found (duh) and it`s boss is the Flame rock monster. It is on fire obviously and reds are advised. Also Bulbmin are found here and they have an onion.

Caves
Dark grounds boss: Dual Dweevil

Forest mines boss: Miners Ghost

Aquarium Garden boss: Dark Force Bulborb