I recommend that you put Tangela, Makuhita/Pancham and maybe Bunnelby if it has huge power. If it does have huge power, it can help you a lot more than Graveler in some situations, but that's up to you. Tangrowth is a fantastic grass type, which your team would appreciate. (Could replace Phantump)
You also might want to pick up something to beat fairies along the way. (Steel/Poison types) Nidorino might be fine, but having two ground types weak to ground wouldn't help too much.
Hariyamais really strong and bulky, and also has amazing abilities. Pangoro is a little stronger and has great abilities, plus that nice dark stab to beat Psychic types. It is also reeeeeally weak to fairies, so watch out for that if Pancham is your choice. :]
Hope I help solidify your team!
PS
I agree. It would be a great addition to your team.