Ru stands for Rarely Used, making it similar to the NU that was used in 4th generation. Sadly this is not that case. Being That I have had roughly over 100 NU battles and maybe 30 or So RU battles, I can safely say this about the two; Though they have similar Pokémon, small changes have changed the tiers drastically. Pokémon that were in OU, BL, and UU in 4th gen are now in RU, only fueling the anger of NU players coming to RU. Some familiar faces like Ninetails, Politoed and Porygon2 have all been moved to OU due to the fact that almost everyone knows Gen 5 is based around weather which is why Ninetails’ Drought ability and Politoed’s Drizzle ability have become Part of the OU crowd. But what of Porygon2? His new ability does help him fit in the OU scene, but it is because of a certain item. This one item defines the RU tier in one simple word. Eviolite.
Until things have been completely resolved, people will be comparing the Gen 4’s NU to the Gen 5’s RU tier. As of now, there is no NU tier in Gen 5, but things are rather similar. Due to the fact that not every Pokémon has been completely sorted out yet (at least to Smogon’s standards); there are hundreds of Pokémon in the RU tier, many of which will probably fall into the NFE tier. But what Pokémon will be able to stand out enough to pass the NFE tier and fit into the RU/Possible NU tier. It will be those that can stand up to stronger, evolved Pokémon and still pack a punch. It is those who can use the Eviolite. For those who don’t know, I should explain.
The Eviolite stone is very similar to that of a choice item. It boosts stats, but at a cost. A choice item will boost one stat but allow one move of the Pokémon respectively. Until now there was no Item that did that for defense. What the Eviolite’s consequence is even though the Pokémon’s defense AND Sp. Def are multiplied by 1.5 that Pokémon must be un-evolved for the defensive boosts to activate. Obviously, not all un-evolved Pokémon will improve very much at all from these defensive boosts but some can. For example, Rhydon. Believe it or not, but Rhydon has a very extensive list of moves it can learn, From Counter to Surf, Rhydon has potential. He has base 120 defense and Base 105 HP. He can use Stealth Rocks for support, then fire off toxic to whittle down opposing team members. What separates him from Porygon2, another Pokémon that is commonly given the Eviolite is the ability to recover damage. Ferroseed is RU, but has access to Leech Seed and has been rumored to be on its way to UU. Dusclops (Who can use Pain Split to steal HP) was immediately put in UU. This is what separates RU Eviolite to UU/OU Eviolite Pokémon. Sadly this is the main thing of RU. Stall power.
Due to the fact that the dust has not completely settled, the RU tier is massive, being the home of roughly more than 450 of the 649 Pokémon. The rest are in LC, UU, OU, and Or Uber. Some new guys that have joined the RU have been causing quite a Commotion, such as Clefable, with a Massive move pool and the ability Magic guard and self recovery. Cresselia, boasting 120 Base HP and Defense and Base 130 Sp. Def to top it off with instant Recovery with Moonlight and increase its offense with Trick room. Lasty, one that I personally find interesting is Dusknoir. Dusknoir does have a lot of Moves that he can learn like Clefable, and he has base 135 Defenses, higher than Cresselia’s. Though he has no recovery outside of rest, he does have Base 100 Attack and can learn all the Elemental Punches (Fire, Ice, Thunder) and has access to Pain Split to deal damage and recover at the same time. Many fans of the RU tier dislike these 3 Pokémon, some with a passion. Mainly because they have become accustomed to seeing them in higher tiers, one in UU and 2 in OU. But these three “pests” are what the main ingredients of RU; Slow and painful battles.
The key components of an RU are as such: Bring 2-4 walls, perhaps a Cleric if you have less walls (due to 5th gen’s new “Wish” mechanics) One scarfed Pokémon , One entry Hazard Pokémon, and a Specs/Banded Pokémon with Max speed to clean up whats left. Not all RU Battles are like this, but from my experience, most of Gen 5 RU matches last roughly 22-30 minutes, while my Gen 4 NU matches lasted 15-20 minutes. If defense is your kind of thing, RU will be fine for you. There is a lot of creativity and Originality that can be done, but grab a drink and something read/watch, because RU matches are not for the hurried battler.