I remember doing calculations on a '16-turn' subseed for use in a Toxic Spikes team, but it's simply not feasible unless the opponent has a HUGE amount of life (I believe it was anything over bulkyDos).
The best abuse definitely goes to lowest HP, highest Spd.
Competitors:
Smeargle: 55/75
Jumpluff: 75/110
Skiploom: 55/80
Sceptile: 70/120
Grovyle: 50/95
With base 50 HP and 0 HPIV, Grovyle has 210 HP.
Add a Leftovers (better than Large Root except in the Blissey Case), Grovyle needs to be leeching back 3/16 of his life a turn (a paltry 39 HP).
With Protect abuse, this gets even more obscene as he only needs to leech 2/16 of his life over TWO turns (13 HP leeched per turn, or 26 once and then they switch). And of course, this is a '32-turn' subseed.
But of course, now the list of problems to resolve.
1) Taunt. If they do, you stop. Ideally you should be using Sceptile who can attack for something. But then again, Grovyle with base 85 SpAtt and in Overgrow might pull out a nasty Leaf Storm.
2) Other Grass-types, or worse, Liquid Ooze. Screw you over. Again you need some sort of attack.
3) Set-up. You ought to be taunting on your own, but only Smeargle gets Leech Seed and Taunt and he should be doing better things. Jumpluff/Skiploom have Encore to solve this problem though and ore viable in this.
4) Speed. 95 base may not be enough and the options are already limited.
It's an overall doomed idea, though if someone pulled off a double Toxic Spike layer and the opponent had no Steel, Poison, Flying/Floating, Grass, Taunt, or Rapid Spin, I'd laugh myself to death.
The Sub/Seed/Protect/Encore Jumpluff does get an award for never dying ever, though.