Based on Ribombee getting Sticky Web, I'm trying to figure out a Webs Ribombee set. Outspeeding and OHKOing Greninja is something Ribombee can do but the old standard, Galvantula, cannot.
Maybe something like this is OK:
Ribombee @ Life Orb / Focus Sash
Ability: Shield Dust
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Sticky Web
- Moonblast
- Hidden Power Ground / U-turn
- Quiver Dance / Stun Spore / U-turn
Sticky Web is a good move, and Moonblast is Ribombee's strongest STAB and has good coverage. Quiver Dance, U-turn, and Stun Spore all hopefully prevent Ribombee from becoming set-up fodder while it lays Webs. Hidden Power Ground has the best coverage with Fairy, IMO, although being unable to hit Celesteela and Skarmory super-effectively hurts. At least you get to 2HKO Heatran (guaranteed without boosting against all variants as long as you use Life Orb). Shield Dust is Ribombee's only good ability.
Ribombee getting outsped and OHKOd by Tapu Koko hurts, though, which is why Focus Sash is an option.