Midosu

The Mids are a group of jellyfish-like boss Reaverbots found in the Nino Ruins, in the Kimotoma Caverns and on Elysium. While they shoot yellow homing energy balls which can be absorbed in to the shield for the shield arm to increase the damage of its shock wave when released the more of them you absorb the more power builds up in the shield arm, and depending if there is water in the room they are in, they gain additional abilities. They can stun you if you collide with them without the Light Barrier.

Nino Island Ruins
Strangely enough, they are not fought as the guardians of the key (Klaymoor instead fulfills that role). This trio is encountered at floor B2, after the room with four giant fish reaverbots. If Mega Man Volnutt drains the water in this floor, the mids will only attack with the homing energy balls, and will not be able to move from their spots. If there is water, they gain additional attacks (see below). The strategy is to just circle them as you shoot with your buster gun, or if you're confident, get closer and use the Drill Arm on them.

Kimotoma Caverns
Since there is no control panel which can be used to drain the water, Mega Man will have to fight them while submerged in water. In addition to the yellow homing energy balls, they can ram Mega Man, turn invincible for a short time and if there is only one of them remaining, drop jellyfish-shaped bombs which explode when touched or when enough time has passed. While circling them is still an option, be cautious of the other Mids that may try to charge you. The room they're guarding contains the Red (S) Refractor.

Elysium
While they fight like they did on Nino Island without the water, it should be noted that gravity has been increased in the room you are fighting in. This can make running away from their energy shots difficult.