Mewtwo fw

1. Mewtwo - runs a variety of sets; gravity mewtwo can create potentially very interesting strategies, especially when coupled with its unnerve ability (i.e hypnosis won't be cured by lum berry). If you want to improve your sucker punch matchup then substitute is a great choice. Unfortunately mewtwo does not have sufficient bulk to ensure that the second hit of kangaskhan's sucker punch does less than 25% (including life orb recoil), so EV spreads for substitute mewtwo sets may be hard to create.
2. Groudon - Again, a variety of sets can be used. If using gravity mewtwo, then precipice blades will be your go-to groudon set. Equally, if you want to use a mixed set then a combination of eruption and precipice blades can suffice.
3. Mega - If running gravity then mega gengar is ideal (hypnosis etc, can be EVd to underspeed mewtwo by a couple points). Otherwise, mega salamence and kangaskhan are good picks, although the former may be of more use (as covered next)
4. Yveltal / Groudon Check - Salamence is a great double mega choice (or single mega if non-gravity mewtwo - substitute or skill swap mewtwo etc) as it can heavily threaten yveltal groudon teams effectively (KOs both with a mixture of hyper voice + double-edge (4 HP yveltal) and draco meteor (12 HP / 4 SpD groudon) if EV'd correctly. Landorus-T is also a great choice in this slot (as shown on Aaron's team), as this deals with groudon well
5. Groudon Support / Big 6 Check - needs to ideally supply a method of speed control, whilst providing a safe lead against big 6. This means smeargle checks are appreciated here, so prankster/fast taunt/lum+safeguard users are really appreciated here. An interesting choice in this slot is jumpluff as used on Keonspy/Kelly Mercier-White's teams (Netherlands regs / UK Nats respectively) as this allows groudon to beat some big 6 lead choices with a greater level of ease with its sleep/rage powder, encore and helping hand support
6. Kyogre / Xerneas Check
Ferrothorn is the main candidate for this slot, as it is able to KO most non-bulky xerneas sets with gyro ball, and with life orb is able to get the KO on bulkier kyogre. If mewtwo holds life orb, then expert belt can work as a back up item.