Hippopotas is notable only for the ability Sand Stream, which makes it the only Pokemon in UU play who can trigger a permanent sandstorm. This set attempts to make the most of Hippopotas's short lifespan by giving it the opportunity to status or scout the opponent's team as a lead. Hippopotas's primary goal, however, is to set up Stealth Rock, which should generally be made a priority over everything else. Yawn and Roar are both effective ways of scouting opponents, one of the few things Hippopotas does well. Protect can block Fake Out and trick U-turners into getting put to sleep when used in conjunction with Yawn. Meanwhile, Toxic allows Hippopotas to damage bulky Pokemon, while Earthquake is better versus fragile Pokemon and Taunt users. The EVs let Hippopotas survive a Fake Out and Return from Ambipom while allowing for maximum attack power should you opt to use Earthquake. The nature and Speed IV allow it to be slower than all Snover, so that sandstorm takes precedence over hail if the two leads are opposing each other.
Hippopotas is the only Pokemon in the lower tiers who can set up a permanent sandstorm, which upgrades it from NFE to a bona fide player in the UU metagame. Although it at first may appear to be a miserable attempt at a lead, Hippopotas actually functions quite well in the role when taking into account its horrid stats. The goal of this set is to play to Hippopotas's strengths, which are essentially limited to setting up Stealth Rock and scouting. Focus Sash allows you to bypass Hippopotas's weak defenses and, against most leads, do both of these things.
In some cases, Hippopotas will be forced to simply use Stealth Rock, then die on the next turn. Such instances will mostly occur against leads whom you cannot switch into for free, or if you feel the need to get Stealth Rock in play immediately. An example of this is when Hippopotas is facing Moltres, who can OHKO it with its special attacks and can U-turn out of Yawn. In other cases, however, its usefulness can extend beyond the first few moves of the game. If Hippopotas sets up Stealth Rock without being damaged, you have several options. When facing a bulky lead like Donphan or Uxie, Toxic is a good option, if you opt for it, to help shorten their longevity. If you wish to scout your opponent's team, Yawn, Roar, or a combination of the two can accomplish this. Yawn will cause most Pokemon to switch, and if they don't, they will be put to sleep. Using Yawn against Pokemon with U-turn should not be done unless you are carrying Protect with it, in which case it is a very sneaky method of putting Pokemon such as Uxie or Scyther to sleep. Because Yawn's effect activates on the second turn, you can use Roar on the subsequent move, which will allow you to scout not one, but two Pokemon, assuming your opponent decides to switch out the drowsy Pokemon. Another option is to simply switch out after using Stealth Rock, thus preserving Hippopotas's Focus Sash, provided your opponent has not set up any entry hazards. This can come in handy later in the game, as it allows Hippopotas to switch into Pokemon like Mismagius and Feraligatr while they are boosting their stats, take a hit and survive due to the Sash, and then phaze them with Yawn or Roar, whichever is most appropriate. Doing this makes Hippopotas a great last line of defense against boosting sweepers, especially those hiding behind Substitutes.
As far as attacking options go, Hippopotas's outlook is pretty bleak. Earthquake is essentially its only viable option, as it desperately needs the STAB. For the most part, however, Hippopotas is too easily 2HKOed to spare many turns firing off relatively weak attacks. However, Earthquake does have its merits against weak Taunt leads, who will attempt to stop Hippopotas from setting up Stealth Rock. If you are more inclined to damage leads like Uxie and spread status in general, then Toxic may be the better option. In the last slot, Roar gives Hippopotas the ability to phaze pokemon with Substitute, as mentioned, which it cannot do with Yawn, and makes it a better overall phazer and scouter. Protect allows you to scout your opponent's moveset, trick U-turners into falling asleep, deal a free turn of sandstorm damage, and block Ambipom's Fake Out, which in turn lets you commit all your EVs to Attack if you wish to do so.
Hippopotas's greatest fears are Taunt, Trick, and weather leads, and it may be in your best interest to switch out against all three. Taunt leads completely immobilize sets without Earthquake and stop those with Earthquake from setting up Stealth Rock. Even though they do nothing to prevent Stealth Rock, Trick leads are also troublesome because they can steal Hippopotas's Focus Sash and later Trick it to another one of your Pokemon, who will inevitably find it worthless. In addition, Hippopotas will likely be forced to switch and be used as death fodder later on. Opposing weather teams will give your entire team trouble, because although Hippopotas can switch in and negate their weather effect immediately, its terrible defenses only allow it to do this so many times throughout the course of a match. If the opposing lead uses Sunny Day or Rain Dance, Hippopotas should flee the scene before taking any damage so that its Focus Sash is still preserved. Good prediction will then be required to sneak Hippopotas in as many times as possible to negate repeated uses of weather-inducing moves. On a related note, Snover leads have the ability to be slower than Hippopotas and therefore override sandstorm with hail on the first turn. To avoid this, Hippopotas should run a -Speed nature with an IV of 13 to ensure it is slower.
