Omastar outspeeds Jolly/Timid Swellow by exactly one point at plus 2. I went with Surf over Scald because I have seen Pokemon live +2 Scald's purely because it was Scald, and not Surf. It's not Hydro because I don't like missing.
On Quagsire, Curse could be used over Yawn, or alternatively something weird like Stockpile I guess. It also gets Acid Spray, Haze, Seismic Toss, Rest Talk, and Toxic, but I feel like Yawn is nice team support around a Shell Smasher.
Vileplume has 24 Special Attack to guarantee the 2HKO on standard Ferroseed. Moonlight is also better than Synthesis, because reasons. (Fun fact, Moonlight heals more in the sun because the Japanese name for Sunny Day is Clear Skies.) I like HP Fire over Sleep Powder, because I find it to be more consistent, however Sleep Powder is usable.
In info not relating to the team, look at those Pokemon Crystal sprites! They look so nice. Too bad Crystal ruined Pokemon Gold Jumpluff's sprite...
Gold
Crystal