Does a outboard have a compressor? If so what does it do?

Some newer mercury motors do, I'm not a mercury expert so i have no idea why.

it put air into the motor, more air and fuel = more hp. alot of problems with the mercs comp. they like to loosen up and throw oil everywhere.

Think of it as a supercharger or turbocharger both are compressors. Any Direct Injected outboard has them. Merc Opti, Yam HPDI,not sure about SHO, Verado 4 stroke there are others.

Normal aspiration fills a cylinder with atmospheric pressure. Now when you put in air at so many psi in the cylinder compression increases more HP too much it explodes due to the bottom not being able to handle the explosion of the air fuel mix at too much PSI. One fine example of this would be HPDI 1 by YAM injecting air at 1000 psi into the cylinder you better be exact in all operating ranges otherwise they explode just like hundreds did (being nice here) without many hours on them usually less than 100. To be fair they worked this out with ECU updates.