Check
Gardevoir-Mega @ Gardevoirite
Ability: Trace
EVs: 24 Def / 232 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Hyper Voice
- Psyshock
- Focus Blast
- Taunt
An immunity to Draco Meteor and a resistance to Psyshock mean that Gardevoir can take any move Latios wants to go for and fire back with a Hyper Voice. Boosted Psyshock really hurts though and is capable of 2HKOing Gardevoir which is why Gardevoir is only a check. There's some interesting stuff that can happen if Latios is already at +1 SpD, namely Hyper Voice even with a Modest nature does not OHKO Latios at +2 SpD (doesn't even put Latios in range of Life Orb assuming they run 29 HP IVs) and +2 Psyshock can potentially OHKO Gardevoir after Rocks, so that's something to keep note of.
Gardevoir-Mega @ Gardevoirite
Ability: Trace
EVs: 24 Def / 232 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Hyper Voice
- Psyshock
- Focus Blast
- Taunt
An immunity to Draco Meteor and a resistance to Psyshock mean that Gardevoir can take any move Latios wants to go for and fire back with a Hyper Voice. Boosted Psyshock really hurts though and is capable of 2HKOing Gardevoir which is why Gardevoir is only a check. There's some interesting stuff that can happen if Latios is already at +1 SpD, namely Hyper Voice even with a Modest nature does not OHKO Latios at +2 SpD (doesn't even put Latios in range of Life Orb assuming they run 29 HP IVs) and +2 Psyshock can potentially OHKO Gardevoir after Rocks, so that's something to keep note of.
252 SpA Life Orb Latios Psyshock vs. 0 HP / 24 Def Mega Gardevoir: 117-138 (42.2 - 49.8%) -- guaranteed 3HKO
+1 252 SpA Life Orb Latios Psyshock vs. 0 HP / 24 Def Mega Gardevoir: 175-207 (63.1 - 74.7%) -- guaranteed 2HKO
+2 252 SpA Life Orb Latios Psyshock vs. 0 HP / 24 Def Mega Gardevoir: 233-274 (84.1 - 98.9%) -- 75% chance to OHKO after Stealth Rock
232 SpA Pixilate Mega Gardevoir Hyper Voice vs. +1 0 HP / 0 SpD Latios: 278-330 (92.9 - 110.3%) -- 62.5% chance to OHKO guaranteed after Stealth Rock
232+ SpA Pixilate Mega Gardevoir Hyper Voice vs. +1 0 HP / 0 SpD Latios: 306-362 (102.3 - 121%) -- guaranteed OHKO
+1 252 SpA Life Orb Latios Psyshock vs. 0 HP / 24 Def Mega Gardevoir: 175-207 (63.1 - 74.7%) -- guaranteed 2HKO
+2 252 SpA Life Orb Latios Psyshock vs. 0 HP / 24 Def Mega Gardevoir: 233-274 (84.1 - 98.9%) -- 75% chance to OHKO after Stealth Rock
232 SpA Pixilate Mega Gardevoir Hyper Voice vs. +1 0 HP / 0 SpD Latios: 278-330 (92.9 - 110.3%) -- 62.5% chance to OHKO guaranteed after Stealth Rock
232+ SpA Pixilate Mega Gardevoir Hyper Voice vs. +1 0 HP / 0 SpD Latios: 306-362 (102.3 - 121%) -- guaranteed OHKO