From the Super Mario Wiki
Flounderflages are red or green flounders with yellow underbellies that appear in Mario & Luigi: Dream Team. In the field, Flounderflages camouflage themselves into the sand, give chase to Mario and Luigi upon sight, and becoming more visible once doing so.
In battle, Flounderflages begin by blending in with the sand, thus rendering them harder to see. They can attack by sliding steadily into a bro without pausing, which can be jumped over. They may also stop before the bro they are targeting to compress themselves and shoot themselves forward, first pointing either at the bro or at an angle that would overshoot the bro, and flinging itself in that direction. If the Flounderflage points at the bro, it must be jumped over. If not and it aims over the bro, he can simply idle to avoid it. The color on the back of a Flounderflage warns the player which bro it will attack when it does; red for Mario, green for Luigi. Additionally, Flounderflages may spawn out of the sand over the course of battle. Navy Flounderflages are rarer, only found in the Torkscrew battle when Mario or Luigi are being chased by Torkscrew's drill.
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