That's right: From June 3 to July 2, there'll be a post each day highlighting Teenage Mutant Ninja Turtles canon immigrants. Now, because TMNT canon is a little confusing, it can be hard to tell what counts as a canon immigrant and what doesn't. So for the purposes of this blog, a TMNT canon immigrant is anything (a) from the movies, cartoons, video games, toy lines, or tie-in comic series that later appeared in (b) TMNT volumes 1, 2, or 4 [because they're by the original creators] or TMNT volume 5 [because the original creators are involved, it's the new official continuity, and its goal is to use as much of the diverse TMNT lore as possible].
Dreadmon first appeared in Teenage Mutant Ninja Turtles Adventures #15 (September 1990). Despite going on to become a Mutanimal, he's not actually a mutant. He was turned into a wolf creature by a magical talisman.
Dreadmon would later go on to cameo with (most of) the rest of the Mutanimals in Mirage's Tales of the TMNT #58 (May 2009), although it's important to note that this is still the "animated" version because it's in a scene of the multiverse.