I need to create a huge amount of entities, but i have to remove a lot of them at the same time, and that destroy the FPS.
Is it posible to declare a new kind of entity,"lighter", so when I remove them it wont be too laggy?

What are you doing with them?
You could use particles with lifespan

The usual approach here is to cache the entities and recycle them, i.e. make unused entities invisible and passable and reuse them when new entities are required.

maybe this helps too (ent_preload):
http://www.conitec.net/beta/aent_preload.htm

do they still use the same memory space if they´re passable and invisible?,

All your c_trace functions will not loop through them for impact, also the renderer will not loop through them, this will save 80%of your memory

it won't save 80% of memory, it wont even save 1%
setting passable and invisible just reduces collision and render speed
to get lesser memory usage, try to use Uhrwerks method
recycle the entities, don't create new ones

and use enable_polycollision = 0; if 1 is not essential...

I don't know what you mean by memory space. If you're talking about the address, yes, it remains the same of cause. PASSABLE and INVISIBLE are just two flags. They can't reallocate memory.

yeah, and memory
he wasnt talking about the amount of memory, hes talking about allocation address of the memory, as destroying, and creating memory sections is a slowish process. What your referring to is a savings in cpu processes.

still will help though