Horrid Rat familiar

[Sir_Chivalry]

One of my players (wizard 5) wants a horrid rat he found to be his familiar, and I'm inclined to allow him

The Horrid Rat is an animal companion available at 4th level to druids, but obviously the improved familiar list is less filled with random animals

Would simply taking the Horrid Rat stats and applying the familiar boni (minus 3 character level since the Horrid rat is a level 4 animal companion) work well enough? Are there any major issues with this approach?

[Dusk Eclipse]

I'd go with making it an Improved familiar option and let your player have his full CL for familiar abilities, unless you are heavily investing in your familiar (or are a gish) they are more often than not a hindrance.

[Sir_Chivalry]

Oh wow, just realized Improved Familiar doesn't reduce effective level for higher level familiars. Guess that's because you need a feat to get it.

I don't see the rat doing much but it's got acid and whatnot so that's going to be fun.

[ShurikVch]

How about the Wilderness Companion (http://www.d20srd.org/srd/variant/classes/variantCharacterClasses.htm#sorcererWizard) ACF?