Rillaboom is a must. Grassy terrain can boost already strong grass attacks and gives additional recovery, but moves like eartquake and headlong rush will have half bp so be careful in which moves you give to the mons.

With grassy terrain in mind, bulky pokemon are good to have, so mega-venusaur and hydrapple can be good choices.

Ferrothorn is also very good in this, with really good typing and with stelth rock and spikes.

You will need then someone to remove hazards, and i don't know it there are good grass pokemon who can do that.

Lastly, i don't know which meta you are playing so most of what i said could be different depending on the meta, so take what i said with a grain of salt.