This level is very hard from the yellow door. A lot of luck needed to complete it without death.
Those roaming drillers and red hulks are unpredictable. Also you cannot farm the spawn points because they are at inconvenient places.
The safest bet is activate the matcens 3 times so they finish producing, while destroy any bot that comes out. When done go back to recharge and pick up the cloaking device, use mega missile to clear the right matcen, while still cloaked kill any drillers you see with homing missile. Since your cloak will elapse soon prepare to pick up the next, and continue your hunt for drillers from behind. There should be a third cloaking device somewhere as there are lot of cloaked drillers that like drop them. Use it and switch to mega missiles to clear the red hulks near the red key.
This is mostly ad hoc as enemies totally unpredictable there. secondary lifters may ambush you, drillers come up too early, or you may run straight into a red hulk first time you enter... A lot of luck needed.
But trials have not ended yet, beyond the red door there are two defense prototypes, and 2 traps. You should try lure the pink robots, because after moving the beyond the trap door there is no return. Otherwise if they surprise you, you need to fight a melee combat with them, which means an instant death... And you can't go backward due to the trap door.
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