I bet that Bellsprout could indeed sweep an entire team of Feebas.
Just wondering, what is the logic behind the Life Orb? Bellsprout have miniscule HP.
That's why Life Orb is good. Anything is going to OHKO Bellsprout anyway, so why not increase your damage on the off chance that you do get to attack, since losing 10% health will never make a difference.
Edit: I see I was beaten to this.
Another option would be an Endure/Custap set. This would ensure that Bellsprout actually does get to hit something most of the time. You bring in Bellsprout safely, then use Endure. Custap Berry activates and you then get to fire off one attack with pseudo-priority. The set could look like:
Bellsprout @Custap Berry
Modest nature
4 HP/252 SpA/252 Spe
Endure
SolarBeam
Sludge Bomb
Hidden Power Ground/Energy Ball
Ideally, you want sun support. With Chlorophyll, Bellsprout will sometimes outspeed an opponent and be able to fire off a SolarBeam without using Endure. If you do not want to use Sunny Day, simply replace SolarBeam with Energy Ball and run both of the other two attacks. You can also use Grass Knot in place of Energy Ball, depending on preference.
The Poison/Grass combination, which takes advantage of Bellsprout's STABs, is resisted only by Poison and Steel. HP Ground takes care of both. If you like, you can run both SolarBeam and Energy Ball instead of HP Ground, which will remove the perfect neutral coverage but give Bellsprout the opportunity to use Grass, its best STAB, even without Sunny Day support.
Some calcs:
SolarBeam vs. Offensive Suicune: 74.8%-88.3%
Energy Ball vs. Lead Swampert: 104%-122.8%
SolarBeam vs. Lead Swampert: 155.4%-184.2%
Sludge Bomb vs. Lead Celebi: 60%-70.6%
HP Ground vs. Scarf Heatran: 74.3%-87.9%