Donphan

Ground is one of the strongest types in the game currently, which is very bad news for Donphan. This is because it's way behind the standard of the day. It can work, but it shouldn't really be used.

Best PvE Offensive Moveset

• Mud Slap and Earthquake is the optimal moveset for an offensive Donphan. 
• Charm and Play Rough work if you're desperate for Fairy coverage
• Tackle, Counter, Heavy Slam, Body Slam, and Trailblaze have no real value here.

Best PvE Defensive Moveset

• Charm is one of the best Fast Moves on defense, and arguably the optimal choice. 
• Mud Slap has neutral damage that compares directly with Charm post-stab, though its coverage tends to be a bit less important.
• Counter and Tackle pale in comparison.
• Body Slam has 3 bars and great neutral coverage
• Trailblaze has valuable counter-coverage for Water Types
• Iron Head threatens Ice Type counters
• Play Rough heavily damages common Dragon and Fighting Types
• Earthquake hits hard, but Donphan probably won't have a shot to launch it.

Mud Slap has STAB, excellent damage output, and reasonable energy gain. Counter used to be great, but it is now an underwhelming option for Donphan after its nerf in Pokemon GO: Max Out. Charm is a niche choice allows Donphan to deal consistent Fairy-type damage. Tackle is the worst overall option.

The addition of Body Slam following the GBL Season 10 update is an improvement for Donphan, enabling it to access a decent Charged Move without consuming a large amount of energy. Trailblaze provides coverage against Water-type Pokemon, and its Attack boost can make Mud Slap even more oppressive. Play Rough is run to handle Dragon-types (and have great neutral damage). Heavy Slam is cheaper and effective for shield baits, but doesn't provide meaningful coverage. Earthquake is largely redundant with Mud Slap already dealing heavy Ground-type damage.