Pretty good team there. Let me suggest a few changes:
Mamoswine - Perfect.
Talonflame - Talonflame is too frail to run this set, in my opinion. If I were you, here's what set I would have:
Talonflame @ Choice Band
Ability: Gale Wings
EVs: 252 HP / 252 Atk / 4 Spd (or invest more in Speed if you want; HP EVs are good though for taking recoil)
Adamant Nature
- Brave Bird
- Flare Blitz
- U-turn
- Steel Wing
Swords Dance and Roost aren't very good choices for something as frail as Talonflame. If you choose to do the set I recommend, make Talonflame your lead and then set up SR with Mamoswine after he faints.
Breloom - Having an Expert Belt honestly isn't that good of a choice if you're only running two Attack types. Consider changing the item to a Big Root or a Fist Plate. It looks good besides that.
Blastoise - Perfect, except Hydro Pump is lacking in accuracy. Water Pulse would be better for this place since it gets the same power as Surf with the ability's boost, and it can cause confusion.
Gengar - If I were you I'd trade Substitute for Destiny Bond and give Gengar a Focus Sash to play it safe. That way, it can either sweep or reliably set up a burn and/or take something down with it. And since you already have a status-inflicting move, switch Sludge Bomb with Sludge wave for added power.
Last Pokemon - If you'd like a Pokemon that resists Gengar's weaknesses, get a Dark-type. They resist Psychic, Ghost, and Dark, and are weak to Gengar's resistances: Fighting, Bug, and Fairy. If you are looking for a tank, choose Umbreon.
If you want something specially offesnsive, choose Zoroark. (Zoroark is especially good to use if Gengar is last in your party. That way, your opponent will try to use super effective moves and end up failing.)
If you want a mixture of the two, choose Hydreigon. It has a great movepool, and its stats let it hit with lots of power and take some hits as well.
So there's my ideas on how you could improve the team. If you have questions (or anything else), please leave a comment and I'll do my best to get back to you. Hope I helped!
EDIT: I went to bed before I finished making this answer, and while I was asleep I guess someone else rated it. I guess you're just lucky enough to have multiple perspectives on the team. :D
