Monster vs Monster

[Dovahkiin]

Werewolf because he looks cooler.

Jason

Vs
30 Nazi Zombies

[DJ Pu$$yface]

Jason

The Silence


VS

Weeping Angel

[boostedlsj]

Not really a monster but.....

Engineer from Prometheus VS. Mr. Black

[Dovahkiin]

I haven't seen Prometheus yet. (I live in America) so Mr. Black.

Xenomorph

VS

The Thing

[Terx2]

Thing

Predator

vs
Jeepers Creepers

[Dovahkiin]

Predator

Xenomorph Horde

VS
Locust Horde

VS
Necromorph Horde

[Sinister Serenity]

DAMN! That's a tough one.
I would say Xenomorph horde because of the acid blood.
Also, they could use members of the other two hordes as hosts.

Necromorphs
Vs
Crawlers

[Cap. Fitzgerald]

Necromorphs

The Creature from the black lagoon

vs

Dracula

[OmegaZilla]

Not knowing what Dracula we deal with (assuming the 1992 one), I say him either way.

The Deep Star Six creature


VS

The Kothoga

[DJ Pu$$yface]

The first creature.

Daleks


VS

Cybermen

[OmegaZilla]

DALEKS ARE SUPREME

Abomination


VS

Gwoemul

[Dovahkiin]

Abomination in a second.

Engineer


Vs

Praetorian

[OmegaZilla]

Ugh. Praetorian.

Alien vs Predator 

[Dovahkiin]

Alien 

Reptile


VS

Predator

[Nightmare Asylum]

Reptile. I'll just spam acid-spit at the Predator

Kane's son (Alien) vs Shaw's child (Prometheus) [no pictures included so as to avoid potential Prometheus spoilers]