Since rain got nerfed in the generation shift, Hydration isn't as useful as it could be. That and Goodra is walled badly by Fairies:
-Draco Meteor
-Fire Blast/Muddy Water
-Thunderbolt/Earthquake
-Dragon Tail/Earthquake
Nature: Quiet/Sassy
EVs: 248 HP/252 SAtk/8 SDef
Item: Assault Vest
Ability: Gooey/Sap Sipper
or
-Draco Meteor
-Fire Blast/Muddy Water
-Thunderbolt
-Focus Blast
Nature: Modest
EVs: 248 HP/252 SAtk/8 SDef
Item: Choice Specs
Ability: Gooey Sap Sipper
If you insist on keeping Hydration, Hydration wall Goodra should look something like this:
-Dragon Pulse
-Thunder
-Toxic
-Rest
Nature: Calm
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Hydration
Stone Edge doesn't give Mawile noteworthy coverage, apart from Talonflame and Charizard Y, who are hit hard enough by Sucker Punch:
-Play Rough
-Sucker Punch
-Knock Off/Swords Dance/Iron Head
-Substitute/Swords Dance
Nature: Adamant
EVs: 132 HP/252 Atk/124 Spe
Item: Mawilite
Ability: Intimidate
Swanna is very subpar in OU. It has little offensive presence and mediocre defenses. Even with investment, it falls to just about any decently powered move, especially Electric moves. Politoed is pretty much mandatory on rain teams for the setup-free rain:
-Rest
-Sleep Talk
-Scald
-Toxic
Nature: Calm
EVs: 252 HP/4 Def/252 SDef
Item: Damp Rock
Ability: Drizzle
or
-Hydro Pump
-Ice Beam
-Focus Blast
-Hypnosis/Psychic/Scald
Nature: Modest
EVs: 172 HP/252 SAtk/84 Spe
Item: Damp Rock
Ability: Drizzle
If this is a Showdown! team, give Excadrill Iron Head over Swords Dance to smash Fairies with and have a secondary STAB.
Xatu is subpar, tbh. I don't think you need 2 hazard removers, so I think it may be a better idea to include another rain abuser, like Kingdra or Tornadus (either form works):
Kingdra:
-Hydro Pump
-Draco Meteor
-Rain Dance/Outrage
-Waterfall/Surf/Ice Beam
Nature: Rash/Modest
EVs: 64 Atk/252 SAtk/192 Spe
Item: Life Orb
Ability: Swift Swim
or
-Hydro Pump
-Draco Meteor
-Scald
-Ice Beam/Dragon Pulse/Sleep Talk
Nature: Modest
EVs: 24 HP/252 SAtk/232 Spe
Item: Choice Specs
Ability: Swift Swim
Incarnate Tornadus:
-Rain Dance
-Hurricane
-Superpower/Focus Blast
-Taunt/Knock Off
Nature: Naive/Timid
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb/Damp Rock
Ability: Prankster
Therian Tornadus:
-Hurricane/Air Slash
-Superpower/Focus Blast
-Knock Off
-U-turn
Nature: Naive
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb