Okay, this is a pretty nice Team you have here. I hope you can get the Egg Move I will recommend here for a replacement of Luxray. Luxray seems off here since it has the Attacking power, but it is too Slow to start a Sweep and too frail to take a Hit. Here we go now.
Luxray-

As I said in the beginning, Luxray seems off in this Team and I suggest replacing it. It's too frail and slow to do anything at all. If you suggest to keep it, replace it Swagger with Ice Fang if possible. If not, I suggest replacing Luxray with:

Tentacruel
Tentacruel can outspeed and sweep while supporting your Team with Toxic Spikes and Rapid Spin! It can also take a hit on the Special Side with that amazing 120 base Sp. Defense. I suggest this for Tentacruel:
Tentacruel@ Black Sludge
Trait: Liquid Ooze
EVs: 252 HP, 212 Sp. Defense, 46 Speed
Nature:(-Attack +Defense)
- Toxic Spikes
- Rapid Spin(Egg Move)
- Scald
- Ice Beam
Tentacruel supports your Team with Toxic Spikes which helps Crobat a lot and Rapid Spin support which is nice. Black Sludge is double Leftovers recovery. EVs give it bulk on the Special Side. That is my recommended Tentacruel.
Cacturne:

Cacturne is pretty good. Switch Cacturne's Nature to Adamant because you need that extra Power. Replace Faint Attack with Swords Dance for double the power and replace Payback with Needle Arm for Grass STAB. Give it a Focus Sash as an Item.
Crobat-

Crobat needs a change. You have the Toxic+Venoshock strategy but you are running Physical Moves with a bad Nature. Replace it with:
Crobat@ Life Orb
Trait: Inner Focus
EVs: 252 Sp. Attack, 252 Speed, 4 HP
Modest Nature:(-Attack +Sp. Attack)
- Venoshock
- Giga Drain
- Heat Wave
- Taunt/U-Turn
That is better. Life Orb makes these moves more powerful. Choice Specs is an option but not recommended. Because of Tentacruel, Toxic is no longer needed on Crobat and can run Venoshock. Giga Drain covers Rock Types. Heat Wave covers Steel Types. Taunt makes it a great stall Breaker. U-Turn is for switching out.
Mamoswine

Really good Mamoswine! Just replace Reflect with Rock Slide to make it perfect.
Magmortar

I suggest Magmortar be replaced because of that Speed. Also because it is outclassed at what it does and it has a limited Movepool resulting in running bad Moves. I suggest replacing it with:

Volcarona
Volcarona has a better Movepool than Magmortar and it outclasses it as a Special Sweeper by a lot. i recommend this Moveset for Volcarona:
Volcarona@ Leftovers
Trait:Flame Body
EVs:252 Sp. Attack, 252 Speed, 4 HP
Modest Nature:(-Attack +Sp. Attack)
- Quiver Dance
- Bug Buzz
- Fiery Dance
- Psychic
Standard Volcarona.Quiver Dance boosts its only needed stats, Fiery Dance and Bug Buzz are its primary STAB. Psychic covers the Fighting Types that carry Stone Edge.
Gallade

Nothing is wrong with Gallade specifically, but i want to try out this Galllade:
Gallade@ Leftovers
Trait: Steadfast
EVs: 240 HP, 224 Sp. Defense, 46 Speed
Careful Nature:(-Sp. Attack +Sp. Defense
- Bulk Up
- Drain Punch
- Shadow Sneak(Move Tutor)
- Substitute
I'm sure you have heard of this set, so try it.
Good Luck with Your Team :)