Donphan has an interesting history as a Pokemon. It alongside Marill and Snubbull was one of the first new Pokemon ever teased for a future generation in the first Pokemon Movie:
It was also a potent gen 2 Ground type possessing excellent HP, attack, and defense, though it was unavailable in Gold version and even in Silver you had to wait until your 8th badge to catch it via its adorable pre-evolution Phanpy. However, in Crystal version if you went looking in the wild grass in the Route just north of New Bark Town that is blocked by cliffs in the morning you could catch yourself an early Phanpy for your team. What a deal!
Donphan sadly lacks the reliable recovery it needs to serve as a great tank for your team, which feels like a waste given how weirdly wide its movepool is possessing attacks like Ice Shard, Seed Bomb, and the elemental fangs. It's also sadly outclassed by its own past and future paradox forms in Great Tusk and Iron Treads.
But Donphan is still a greatly respected Ground type at least in my eyes, and can still lead you to victory despite what naysayers may say.
Tactical Elephant
Ability: Sturdy
Item: Assault Vest
Nature: Adamant
EVs: (HP 252) (Attack 252) (Defense 4)
Tera Type: Ground, Ice, or Steel
Moves:
Earthquake
Stone Edge
Knock Off
Fire Fang/Ice Shard/Play Rough/Seed Bomb
Set Details:
Slap on an Assault Vest to give extra special bulk and go to town. Earthquake is your reliable STAB, Stone Edge is powerful and has great coverage with Earthquake, and Knock Off is great neutral coverage and perfect for item reliant opponents. The last slot is your choice since Fire Fang handles Scizor, Ice Shard offers priority and a nasty surprise for the x4 weak pseudo-legendary Dragons, Play Rough offers coverage against Fighting, Dragon, and Dark types, and Seed Bomb surprises the Water/Ground threats. Invest everything into physical attack and HP for max power and bulk. Tera typing can go to either Ground for stronger Eartquakes, Ice for a much stronger Ice Shard in terms of base power and the added STAB, or Steel to bestow better defensive typing and a means to survive an oncoming Grass or Ice attack.