After playing around for a bit I am going to nominate that ferrothorn to move from B to A- if not A rank.
Ferrothorn @ Rocky Helmet
Ability: Iron Barbs
EVs: 252 HP / 88 Def / 168 SpD
Relaxed Nature
IVs: 0 Spe
- Gyro Ball
- Power Whip
- Stealth Rock
- Leech Seed
OR
- Stealth Rock
- Spikes/Leech Seed/Thunder Wave
- Protect/Power Whip
- Gyro Ball/Protect
This thing can be a literal pain to deal with. With linked moves doubling your chance to take barb and helm damage along with possible 1 turn setup of hazards, this thing can be exceptionally annoying to try and beat. This mon can also deal with a decent amount of the top threats as well. Talonflame takes lifetimes of recoil from barbs, helm and brave bird recoil, taking over half of it's health from all of that. If clefable is running it's most common set -
Cosmic boiled with unaware- Then it cannot touch it due to both of it's attacks being resisted and taking residual damage from leech seed, hazards and stab gyro ball. To top that all off, 4 or 5 of the A+ rank mons get destroyed by this thing's recoil damage -
with aegi being the only one that doesn't care as much and zard x can kill a lot easier but still takes helm and barb damage-
Tl;dr Ferro should be A- at least due to it's ability to set up hazards and deal extreme amounts of damage with rocky helmet and iron barbs combination.