One think to check before suggesting a mon, is what threats are dangerous for our 5-man team, and if a sole poke can cover the most important of them. For example if we go for Pocket's Deoxys-D, then SD Terrakion, RP Genesect, any Volcarona, CM Keldeo, Garchomp, DD Gyarados and Sandslash in sand (yeah don't laugh, because as of now it can sweep the whole team with one SD under his belt) all become very huge threats. Can we cover most of them in the last slot? The answer is of 'course no. The problem with Deoxys-D, is that he can get set-up on by many faster pokes, and because we have no scarfers or strong priority, not even very fast pokes (SD Garchomp sweeps us), one turn of set-up could very well mean gg. My opinion is that we should find something that leaves little to zero set-up room, while also having SR, which is a must and i don't want us to be forced to use it in our last mon, as this would limit us greatly. So for now here is my suggestion:
Terrakion @ Life Orb
252 Atk / 4 SpD / 252 Spe
Jolly nature
- Close Combat
- Stone Edge
- X-Scissor (replaced SD after ginganinja's suggestion)
- Stealth Rock
With Terrakion we get a lot of offensive pressure, which means that the opponent will have a hard time setting up on this beast. It is also very fast allowing us to revenge kill troublesome threats, such as Garchomp, opposing Thundurus-T, Landorus and also speed tie with the 108 base speed group. It also can ohko everything at team 2. Terrakion can easily set-up SR against Heatran, or if he forces out Mamoswine. Finally it provides us with a fire type resistance and thus a Volcarona counter, which is very important. The 4 SpD evs are there so that Genesect doesn't get the SpA boost. I think that Terrakion fits like a glove!