I have a 2 bathroom, a big bathroom and a small bathroom.The small bathroom has a smell like something died in it. I cut the insulation away on the bottom of the bathroom there was nothing under it. Could it be a clogged vent causing gases to come back in the house or a dead mouse since we have cats? I have never seen a mouse but the smell is strong in the bathroom.

The P-trap in the sink and the shower may have dried up and is allowing sewer gas to backdraft. Simply run the sink and shower for a few minutes to refill the P-trap. If this bathroom isn't used that often, make it a point to run the water for a few minutes, every couple of weeks.

We checked the p-tap and filled them but it still smells.

Another thought would be a bad wax ring on the toilet allowing sewer gas to seep out around the toilet.
However, these types of homes are notorious for having the drain pipe fall of the connection to the toilet under the home.

When i tore off the insulation, everything was dry including the toilet drain.

Manufactured housing builders sometimes use a mechanical vent rather than vent to the outside. You will find the mechanical vent under a sink just kinda sticking up there by itself. It will have a top on it and slots in the sides of it, there is a spring mounted stopper inside it that allows the discharge to pull air in behind it to keep down the gurgling. The spring rusts out and the vent stays open, allowing odors. Normally you can just unscrew the mechanical vent, take it to a mobile home parts house and get a new one.

Well, may be something died. So you should keep your vent ventilated and completely packed so that nothing enters into it.
And do keep checking vents at a regular interval of time. So that your house will be clean and supplied with clean air.

If the bathroom isn't used that often, and make it a point to run the water for a few minutes, every couple of weeks.