The best way to succeed at this level is to stay flying and use long range attacks. Its better to be GL at this point as M Manhunter has a crap long range. When you run out of power, wait until you are fully recharged before attacking again. Focus your attacks on the monsters that come out of one portal. Otherwise you get surrounded.

The monsters climb out of the blue water (which hurts you if you stand in it, so when you start up a combo and move forward you have to jump back out of the water) Every time you kill one monster, another climbs out of the water. Move all the way down to the bottom and fight them one at a time. Let MM die if you want to, it doesn't matter. When the pool closest to you runs out of monsters, walk forward to the next one. Before killing the last one, fly around till your blue meter fills. When the scorpion thing comes at you, use Detention Cage and hit it with Plasma blasts over and over. In 1-player your partner runs around getting hurt. This level can be beat with GL only.