First time nominator, I'd like to nominate
Diggersby to C. I know what you're thinking - he's outclassed as a wallbreaker ground-type by Zygarde, and he's outclassed for versatility and scarf variants by Landorus - and yes, to some extent, you're right. However, Diggersby takes on Tapu Bulu, Tangrowth, defensive Lando-T, Mega-Slowbro, Ferrothorn much better and actually becomes a terrific breaker for Zygarde/Lando to sweep later on. This is the set I run and a few relevant calcs:
Diggersby @ Normalium Z
Ability: Huge Power
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- Earthquake
- Return
- Swords Dance
- Agility
+1 252+ Atk Huge Power Diggersby Breakneck Blitz (160 BP) vs. 252 HP / 216+ Def Landorus-Therian: 402-474 (105.2 - 124%) -- guaranteed OHKO
+2 252+ Atk Huge Power Diggersby Breakneck Blitz (160 BP) vs. 248 HP / 212+ Def Tangrowth: 429-505 (106.4 - 125.3%) -- guaranteed OHKO
252+ Atk Huge Power Diggersby Breakneck Blitz (160 BP) vs. 0 HP / 4 Def Tapu Bulu: 298-352 (106 - 125.2%) -- guaranteed OHKO
Obviously this proves nothing on it's own, but if you can get it in on Magearna, Heatran, Ttar, Chansey etc etc. Digger can easily set an SD up and kill the ground resist. Agility allows it to sweep later on or if you predict something faster to come in, or you want to go for game, Agility lets you hit 510 speed to pick off faster threats.
Yes, double dance Flyinium Lando is probably better, but Digger can continue to spam Return after using his Z-Move, which is incredibly useful if you want to come in later to sweep with Agility, or to pick off weakened flying threats, or if the opponent predicts your Z-Move and you need a powerful STAB. He also melts Hp Ice Zapdos, and can bluff Quick Attack if you're an absolute madman.
I'll link a few replays to show you I'm not talking complete shit, but I don't have too many as I was low ladder for a while and won't waste your time showing you him beating full eeveelution teams. Alexidiaz is a good player, the other guy... I'm not so sure. But don't let my rank alone make Digger look bad, he was a huge part of getting me into the 1600+ region on the ladder. Try him out.
http://replay.pokemonshowdown.com/gen7ou-593487705 Digger cleans at +2 speed
http://replay.pokemonshowdown.com/gen7ou-589961020 Digger breaks through Tangrowth without an SD and breaks massive holes.
I've clearly oversold him - I nommed him to a C rank for a reason. Mediocre speed, little bulk and poor defensive typing, as well as being walled completely by Skarmory etc (however on Celesteela: +2 252+ Atk Huge Power Diggersby Breakneck Blitz (160 BP) vs. 252 HP / 0 Def Celesteela: 329-387 (82.6 - 97.2%) -- guaranteed 2HKO after Leftovers) recovery are problems. He does need a Z-Move too, which is a problem, but he makes a great partner for Zygarde and Koko - he punches holes in the things that stop them and can usually come in on the things Koko attracts. Fast scarfs outspeed him even at +2. He's generally outclassed by Lando, but I think he has enough of a niche (and maybe surprise factor) to put him in the lower tier of the rankings.
Feel free to disagree - I imagine as a relatively lower tier player this is a little bit above my station but I hope I made some genuine points :)