YA Book About Monsters from Another Dimension

[Kyle]

I read this in the last 90's and it seemed to be written and set at about that same time.
I want to say it was written by a husband & wife team but cannot be sure.

The parts I remember is a teenage boy meets some sort of Monster that is like a Yoda w/ sharp teeth and he needs his help defeating other mosters that come out of a portal. Each monster/creater has its own powers/physical abilities.

[Capn]

Hey Kyle,

Any memory where the portal is located? Or the setting of the story (USA? NYC? Timbuktu? Hey, you can never tell!). :)

Do you think it could have been part of a series?

Was it illustrated?

[Kyle]

It was set in a nondescript American town. I think I recall their being at least one sequel.
It wasn't illustrated but there was either an inset of companion book w/ diagrams of some of the creatures.