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Hell hounds are CR 3 - which means an average party of that level will find it a challenging encounter. That's for a single hound, and you want them to face 4 of them? Hell hounds do 1d8+1 plus 1d6 fire damage per hit not to mention their 2d6 cone shaped breath weapon. Against a level 2 party (even assuming they have maximum HP) they are going to do a whole lot of damage in a short amount of time. Potentially they could down a party member about once a round.