Generally, I assume untyped ongoing damage to be caused by bleeding.What causes the ongoing 3 damage?
You can still make it work with the given description.
Some of those rats go with him OMNOMNOM.
And some get shaken off mid-teleport. Somewhere in the Feywild a gnome family is sitting down to eat, and some Eladrin pops in momentarily, standing on their table, then vanishes, leaving behind a dozen rats...
"Hooray, dessert!"