This site is not for solicitation of services or 'purchasing' development. Please do not post requesting side mods/plugins and so on. Your thread will be removed, and you will receive a warning.
-Venusaur has a decent stat distribution, Sludge Bomb to get past many types that resist Grass, and Sleep Powder.
-Whimsicott has Prankster and some annoying moves to take advantage of it. Encore is not implemented though and it's also not very bulky.
-Sceptile can go either physical or special, with extra coverage moves to differentiate it from Serperior.
-Torterra and Leafeon are both physical attackers with some differences in Speed and coverage options.
-Parasect has Spore, but that's all it really has going for it in mono-Grass.
-Exeggutor has the highest immediate Special Attack and Psychic moves, but it has even more weaknesses than other Grass types and is rather slow.
While there are many sun abusers with Chlorophyll and a setter in Whimsicott, many of sun's merits like Growth, Heat Rock, and Weather Ball are unimplemented, so it won't be as good as it is in the games.