I mean if you really need a Second type there's Dark for an obvious one, Steel if you want to emphasize defensive Wall, OR for a really out there typing, Electric.
Assuming that your trying to balance the 3 starters as Mario (Blaziken) Glass Cannon (Infernape) and Mighty Glacier (Emboar) it does not let Emboar play his alloted roll, he can't tank because he's got terrible typing, he can't hit fast because he's naturally slow and he can't match up to either Blaziken or Infernape.
I mean he already couldn't match up to either of them but that was because he had lower stats not because his typing killed him.
Again just my opinion because Samuwott benefits from the Fighting Typing, Serperior is covered in thick juicy love with the Dragon Typing (x4 Weakness to Ice excluded) but Emboar is just getting screwed over.
No mean to offend, I don't know your reasons behind it just... sounds weird.
Well as it were, Fire/Dark was the original plan for Emboar but after not being able to decide if it REALLY fitted it plus the problem of there being no real Dark moves for it (does it look like it can Crunch?) I chose to go for another typing.
Fire/Fighting has been overdone to death on the starters and out of the remaining types, Ground was really the only one that worked (being a pig and all).
While I do have to agree that Emboar isn't quite as useful as Samurott or Serperior, the addition of Sheer Force does still give it some huge power in the form of Flare Blitz, and the STAB (now level-up) Earthquake helps.
As it is, Serperior and Samurott have some very late level up moves which make them incredible (I'll refrain from saying which for now, but you might be able to hazard a guess...) whereas Tepig gets a boost the whole way through thanks to Sheer Force.
That's pretty much all I can explain. It does suck a bit but Emboar's hard to work with. Just keep it out of the way of Water moves and it is fine, though. I did kinda screw the starter triangle up, but Emboar comes in useful for the main game (particularly Elesa's gym) moreso than it did before... I think :x