When and where is the ice cream man put in all of this? Why's he here and where did he come from?

I think the ice cream man is a child molester cause the make him out to be one. I'm not sure where he came from though. But he's most likely a pervert.

He's there so Him can pull off his whole plan. Without that ice cream man...Mimi and Jr. shouldn't have met.

If tu wanted to know where he is from, it's a little comic por Todd MacFarlane called "Spawn"

This is also where is the demon that attacks the kids at the beginning of the framing tale (Violater aka Clown) is from. The dude who helps them out is Spawn himself.

As to why he's in the story, it's up for interpretation but only Bleedman really knows for sure. I'd say that he seems like mostly a background character there for flavour. Extremely dark comic so it fits.

He is probably a misceláneo sign of deviant acts in the world. Grimtales happens to be posed as a kinda "Evil" comic some might say. He represents molestation of children. And tht is one of the seven deadly sins which grim associates with in his job.