Donphan is one of the more reliable Pokémon to consider for any balanced team in UU because of its ability to Spin away entry hazards. The common presence of Stealth Rock and even Spikes in UU makes Donphan ever more popular. Another interesting thing to note about Donphan is its ability to beat just about every Ghost-type you are likely to encounter in UU, ranging from Spiritomb to Rotom. However, the lack of recovery really does hamper Donphan's ability to tank hits repeatedly, and outside of Stealth Rock and Rapid Spin, Donphan has very few support moves to take advantage of. The sturdy elephant is not the most spectacular Pokémon around, but he is a solid and reliable supporter who can hit hard when the need arises.
Donphan is one of the few viable Spinners in UU, with several key traits that make using it advantageous over using Hitmontop and Claydol, such as the monstrous base 120 Attack and Defense stats and the ability to hurt Ghost-types with either Earthquake or Assurance. Donphan, being so physically defensive, also acts as a counter to some of the major physical threats in the metagame, such as Swords Dance Drapion, Swords Dance Toxicroak, and Swords Dance Scyther (assuming you are running either Ice Shard or Stone Edge in the fourth moveslot).
This set revolves around Rapid Spin, which removes any entry hazards your opponent might have laid down during the match, in particular Spikes and Stealth Rock. Earthquake is the main STAB move of choice, as even incoming Spiritomb (a common switch-in to this set) is heftily damaged by it, possibly being 2HKOed after Stealth Rock damage. Assurance prevents Levitating Ghost-types, namely Rotom and Mismagius, from coming in freely, as even the most defensive of Rotom and Mismagius will lose at least 75% of their health from a 100 Base Power Assurance, with Stealth Rock factored in. Finally, the last moveslot is up to preference. Stealth Rock is a useful support option on Donphan, as it gets many opportunities to switch in and cause further trouble for the opponent. Ice Shard allows Donphan to hit Flying-types for a decent amount of damage and allows you to pick off weakened Dragon Dance Altaria and Rock Polish Torterra. Despite Stone Edge's higher Base Power, its mediocre accuracy makes it slightly inferior to Ice Shard.Team Options & Additional Comments >>>
Although Donphan is normally seen as a defensive tank that focuses on taking hits, this set instead focuses on Donphan's base 120 Attack stat and its great STAB move in Earthquake. Choice Band provides Donphan with an Attack stat of 558, which is simply overwhelming against some of the previous set's counters. For example, Spiritomb is always outsped and 2HKOed by Earthquake, while Rotom and Mismagius are always OHKOed by a 100 Base Power Assurance after Stealth Rock damage. Simply put, coupled with an already great physical Defense and an even higher Attack (with Choice Band equipped), Donphan is capable of putting large holes in the opponent's team with little effort.
Earthquake is Donphan's primary attacking option, and it puts a serious hurt on anything that doesn't resist or is not immune to it. Assurance is needed to hit Levitating Ghost-types like Rotom and Mismagius, both of whom enjoy switching into Donphan to block any attempts to Rapid Spin and setting up themselves. The third moveslot gives Donphan an option to hit Flying-types who are immune to Earthquake. Stone Edge has a much higher Base Power than Ice Shard, making it the preferred option, despite the shaky accuracy; nevertheless, Ice Shard is a useful option for its 100% accuracy and ability to prevent Torterra from walling you with ease. For the last moveslot, Rapid Spin is quite a useful option for eliminating the opponent's entry hazards, which is capitalized by this set's ability to beat any Ghost-type one-on-one. If your team does not have much of an issue with entry hazards, then Ice Shard can be used over Rapid Spin as well.Team Options & Additional Comments >>>
Donphan does not have many competitively viable options outside of what has already been mentioned. A combination of Rest + Sleep Talk can be utilized if your team is in essential need of a defensive tank that is guaranteed to last, but the mediocre type coverage between Earthquake and either Assurance and Stone Edge is not enough in consideration of the amount of Pokémon who can potentially set up on Donphan while asleep. Donphan can run Toxic in the fourth moveslot of either of the two sets, but Toxic is largely unneeded when Donphan can simply eliminate common switch-ins with Earthquake or Assurance. A Rock Polish set can be considered, but Donphan lacks the Speed and type coverage to pull off a sweep most of the time. Body Slam can be used to paralyze opponents if you're lucky, but the lack of power is noticeable. Poison Jab hits Tangrowth super effectively, but Tangrowth's massive Defense stat makes it a worthless option. Counter can nab a surprise kill against physical attackers like Altaria. Endeavor and Flail are gimmicky options at best.
On the Rapid Spin set, transferring 80 EVs from HP to Speed will enable Donphan to outpace minimum Speed base 60 Pokemon, such as Clefable and Weezing. This change can have situational utility; for instance, Donphan can Head Smash a weakened Weezing before being burned by Will-O-Wisp.
Checks and Counters
Most Water-types are capable of switching into Donphan with ease and threatening it with a STAB Surf. Both Milotic and Slowbro have enough physical Defense to withstand an Earthquake or two, with the former outpacing Donphan. Ludicolo resists Earthquake and can threaten Donphan with either of its STAB moves. Azumarill can survive one Earthquake and deal heavy damage with boosted Waterfalls. Even Blastoise can come in a few times and KO Donphan with Surf, although the lack of recovery hurts. Poliwrath can also switch into Earthquake with little trouble and deal huge damage with Waterfall in return.
Flying-types are capable of switching into Donphan's Earthquake with impunity and threaten Donphan with boosted attacks, provided Donphan does not have Stone Edge or Ice Shard in the fourth moveslot. Moltres can scorch Donphan with a Life Orb-boosted Fire Blast, and Swellow can easily wear down Donphan with a Guts-boosted, STAB Facade, while Altaria can set up on Donphan with Dragon Dance and proceed to deal heavy damage with Outrage.
Torterra and Tangrowth can switch into any of Donphan's sets with ease due to their mighty physical Defense and KO with a super effective Grass-type attack or stall out Donphan with Leech Seed. Venusaur, while it doesn't resist Earthquake, can switch in and KO Donphan with Leaf Storm, set up Swords Dance, or put something to sleep with Sleep Powder.
Outside of Torterra and Tangrowth, Weezing is the most reliable counter to Donphan, as its high Defense and immunity to Earthquake means that Donphan will hardly be able to land a scratch. Will-O-Wisp also shuts down Donphan completely, further nullifying its attempts to weaken you down. With some EV investment in Special Attack, Weezing can even 3HKO Donphan with Flamethrower or Fire Blast.
In general, a reliable (special) Grass-, Ice-, or Water-type will do a lot of damage to Donphan, so the best counters have such a move as well as a high defensive ability to take Earthquakes / Assurances.