Don't Use This:
Donphan @ Leftovers
Ability: Sturdy
EVs: 252 Def / 252 HP / 4 SDef
Impish Nature
- Stealth Rock
- Rapid Spin
- Earthquake
- Ice Shard
Why It's Bad:
Donphan is the middle child of Landorus-T and Excadrill, with Excadrill being the better offensive Pokemon + Rapid Spin, with Landorus-T being a better Stealth Rock and Defensive Ground-type.
>b-b-but Donphan has a higher Defense than both!
252+ Atk Choice Band Talonflame Flare Blitz vs. 252 HP / 252+ Def Donphan: 150-177 (39 - 46%) -- guaranteed 3HKO after Leftovers recovery
-1 252+ Atk Choice Band Talonflame Flare Blitz vs. 252 HP / 252+ Def Landorus-T: 121-144 (31.6 - 37.6%) -- 0.2% chance to 3HKO after Leftovers recovery
It's nowhere near as bulky as Landorus-T thanks to Intimidate. Play Rough, also, is illegal with Stealth Rock, and it's pathetically weak:
4 Atk Donphan Play Rough vs. 4 HP / 0 Def Dragonite: 158-188 (48.7 - 58%) -- 96.1% chance to 2HKO
4 Atk Donphan Play Rough vs. 4 HP / 0 Def Garchomp: 158-188 (44.1 - 52.5%) -- 21.5% chance to 2HKO
And, fun fact: Play Rough hits Pokemon that are 4x weak to Ice Shard (only Dragon/Ground or /Flying) harder than Ice Shard itself. Donphan is utter shit in OU, stop using it (BAN ME PLEASE). Now in UU however, it's pretty ok. Donphan is just not what it once was in OU, it's just bad, to put it flat out.
Instead, Use This:
Landorus-Therian (M) @ Leftovers / Rocky Helmet
Ability: Intimidate
EVs: 252 Def / 252 HP / 4 Spd
Impish Nature
- Stealth Rock
- Earthquake
- U-turn
- Knock Off / Stone Edge
Why It's Better:
Landorus-Therian has better stats
everywhere bar HP (by 1 point, wow!). Landorus-T fits the role of Defensive Ground-type far better than Donphan, as it can actually be a threat to other things, and has access to U-Turn to become a pivot. Stealth Rock is just done far better by Lando-T and Lando-T's Earthquake is much more powerful than Donphan could ever hope to be. Knock Off is the icing on the cake, and while Donphan has access to it as well, it just doesn't have the room for it. Another key factor of Landorus-T is that is very unpredictable, it could be running Defensive, Scarf, Band, Double Dance, or even Calm Mind or Gravity! It's a very versatile Pokemon backed by tons of power and bulk and eclipses Donphan in just about everywhere bar the ability to Rapid Spin, which is nowhere near as hard to come by thanks to Defog's new mechanics and other Rapid Spinners. Another great selling point of Landorus-T is that it's a lot faster than Donphan and doesn't get outspeed by everything. Overall, Landorus-T is the far superior Defensive Ground-type.