Dual screens, and sub seed are pretty decent sets actually. It's not very bulky for stall teams but it supports stall extremely well while providing offensive potential.
Meh not in OU. You're much better off using something like Ferro or Venu for seeding, and they provide much better defensive synergy with other 'mons, which is something stall loves.
As far as "offensive presence" on stall, why Serp over something like Breloom or, once again, Venu?
There are just much better options for stall and semi-stall. IMO Serp struggles to find a niche.
Dual screens are only really particularly good on offensive teams (at least at a higher level of play), and Lati@s or Azelf are far better choices for that role. I've said this before elsewhere, but team slots are more valuable than ever these days. Why use Serp for screens over the Latis when its bulk and defensive typing are both considerably worse?
Contrary Leaf Storm can be nice when it gets out of control, but I think I'll be sticking to more versatile, less predictable grass types with greater movepool diversities.