(Sorry if my english is not perfect. Its not my first language. And im only 14 so who could blame me?) Okay. Before i start this i know smogon tiering is usage based but some things have niches in OU that can't be exploited in UU or lower so it would actually be worse in UU then in OU. I will give a few examples. First off: Gastrodon. This guy was nu last generation and because storm drain got buffed. People found out that this guy is pretty good in countering water type attacks in OU which are extremely common due to rain being very very common. Even in rain itself its pretty useful. I completely agree with this. But at the start of this generation this guy was NU because his ability cant be exploited that well in the lower tiers. He seriously is worse in UU and in RU then in OU. In NU he does just as well but thats because hes just a good poke in NU. The sets this guy usually runs are: Gastrodon @ Leftovers Trait: Storm Drain EVs: 252 HP / 4 SpA / 252 SpD Sassy Nature +SpD -Spe/Calm Nature +SpD -Atk -Earthquake/Earth power -Ice beam/Scald -Toxic -Recover Gastrodon @ Choice Specs Trait: Storm Drain EVs: 160 HP/36 Def/252 SpA/60 SpD Modest Nature +Spa -Atk -Surf -Ice Beam -Earth power -Hidden power grass Now onto the next poke. Toxicroak. This pokemon heavily relies on weather due to his dry skin ability which heals 12,5% of his HP every turn in rain. In sun however it loses 12,5% every turn. When a dry skin poke is hit by a water attack it heals 25% of its health. When hit by a fire attack he would take 1,25 times more damage then he normally would. In OU this guy is a good sub user but it is however frail. Healing 18,5% (dry skin and black sludge) each turn helps alot but its still easily OHKO'ED. This guy absolutely HAS to be used in rain or hes not even worth using in OU. In UU where no poke has access to drizzle he has to rely on rain dance which is very easy to pull off. So he is worse in OU then in UU. The sets this guy usually runs are: Toxicroak @ Black Sludge Trait: Dry Skin EVs: 244 HP 252 Atk 12 Def Adamant nature +Atk -SpA -Bulk up -Substitute -Drain punch -Sucker punch Toxicroak @ Life orb/Black sludge Trait: Dry Skin EV's 4 HP 252 Atk 252 Spe Adamant nature +Atk -Spa -Swords Dance -Sucker Punch -Cross Chop -Ice punch Next up: Another guy that was nu at the start of this generation. Dugtrio. His sash reversal set did pretty well in nu. His ability arena trap is pretty good too. His speed is amazing. His attack is... meh. And he is very very VERY frail. His only niche in OU is to trap weather inducers and kill them allowing you to win the weather war. Yup thats pretty much it. -.- He's not even very good at this. He is only OU cuz he hits the usage mark. Sometimes i find it ridiculous that this thing is even OU. The sets that this... thing uses are: Dugtrio @ Focus sash/Fighting Gem/Expert Belt Trait: Arena Trap EVs: 4 HP 252 Atk 252 Spe Jolly Nature +Spe -SpA -Stealth Rock -Reversal -Earthquake -Substitute/Stone edge/Sucker punch Dugtrio @ Choice Band/Life Orb Trait: Arena Trap EVs: 252 Atk 32 Def 224 Spe Jolly Nature +Spe -Spa -Earthquake -Stone Edge -Shadow Claw -Sucker Punch Now something else: Amoonguss. This guy seriously checks so many things in OU but in UU however its not so great. In RU it's a decent poke but the sap sippers running around doesnt help. In NU its a very good pokemon hitting very high on the usage stats because the most threatening pokemon in NU are physical and Amoonguss is fortunately a wall that can either go physical or specially defensive. It got Regenerator in the process of BW2 which helped it even more. It got a few good moves that it can take very good profit from. These include Giga Drain, Sludge Bomb, Spore, Stun Spore, Synthesis, Clear Smog, Hidden Power and more. In OU it can cripple and check many pokemon but it nearly doesnt hit the usage mark of rising to OU. Im completely fine with this because it is a solid pokemon in NU as it is. And it has use in OU too. But we dont want this thing raising all the way up to OU just like Dugtrio and Gastrodon did. Here is the set that Amoonguss utilizes very well in OU: Amoonguss @ Black Sludge Trait: Regenerator EVs: 252 HP 28 SpA 228 Calm Nature +SpD -Atk -Spore -Giga Drain -Stun Spore/Clear Smog -Sludge Bomb/Hidden power Ice Next up: Chlorophyll and Sand Rush users. These guys are absolutely threatening in their respective weather. These guys are strong and have below average speed. But that gets really high due to their abilities. In lower tiers than OU permanent weather doesnt excist so they cant shine there like they do in OU. Stoutland is a very good Choice Band user due to his high speed in sand. Sandslash can Swords Dance and has access to EdgeQuake and even spin hazards away. Victreebell and Lilligant can both use Growth and even Quiver Dance in Lilligants case to sky rocket their special attack and attack. They both become a monstrous powerhouse that fire off really high powered Solarbeams and Hidden power fire's or Weather Balls. Victreebell even has the stats to go mixed. The sets that these guys use in their respective weather in OU are: I made this set myself but seriously guys go use this Lilligant: Lilligant @ Wise Glasses Trait: Chlorophyll EVs: 252 HP 252 SAtk 4 Spe Modest Nature +SpA -Atk - SolarBeam/Giga Drain - Growth/Quiver Dance - Hidden Power Fire - Sleep Powder And heres the smogon set: Lilligant (F) @ Leftovers Trait: Chlorophyll EVs: 60 Def / 252 SAtk / 196 Spe Modest Nature (+SAtk, -Atk) - Sleep Powder - Quiver Dance - Giga Drain - Hidden Power Fire / Ice / Rock Stoutland @ Choice Band Trait: Sand Rush EVs: 252 Atk 252 Spe 4 SpD Adamant Nature +Atk -SpA -Return -Wild Charge -Crunch/Pursuit -Superpower Victreebel @ Life Orb Trait: Chlorophyll EVs: 136 SAtk / 252 Spd / 120 Atk Naive Nature IVs: 30 Atk / 30 SAtk / 30 Spd - Leaf Blade - Sludge Bomb - Growth - Weather Ball Sandslash @ Life Orb/Lum Berry Trait: Sand Rush EVs: 252 Atk / 252 Spd / 4 Def Jolly Nature +Spe -SpA/Adamant Nature +Atk -SpA - Earthquake - Rapid Spin/X-Scissor - Stone Edge - Swords Dance I think this sums everything up. Im sure there are more kinds of pokes like this. But im sure you will find out by yourself. :) Ill add more pokemon when you suggest one i like to add.