Help with my Competitive X/Y Team Please?

[ShinyMagcargo]

So I've been playing competitively on and off since 5th gen so I have some experience with the competitive scene but I feel like my team building skills could use some work. My current team has won me some battles so I wouldn't say it is terrible but it definitely has its weaknesses. This is my team as of right now:

Mamoswine @ Focus Sash
Ability: Thick Fat
EVs: 4 HP / 252 Atk / 252 Spe
Nature: Jolly
-Earthquake
-Icicle Crash
-Stealth Rock
-Stone Edge


Tangrowth @ Leftovers
Ability: Regenerator
EVs: 252 HP / 252 Def / 4 spDef
Nature: Relaxed
-Knock Off
-Giga Drain
-Leech Seed
-Sleep Powder


Ampharos @ Ampharosite
Ability: Static (Mega: Mold Breaker)
EVs: 172 HP / 152 spAtk / 100 spDef / 84 Spe
Nature: Modest
-Volt Switch
-Thunderbolt
-Dragon Pulse
-Thunder Wave


Rotom-W @ Choice Scarf
Ability: Levitate
EVs: 252 spAtk / 4 spDef / 252 Spe
Nature: Modest
-Volt Switch
-Thunderbolt
-Trick
-Hydro Pump


Magcargo @ White Herb
Ability: Flame Body
EVs: 248 HP / 8 Def / 252 spDef
Nature: Bold
-Recover
-Shell Smash
-Lava Plume
-Ancient Power


Scolipede @ Black Sludge
Ability: Speed Boost
EVs: 4 HP / 252 Atk / 252 Spe
Nature: Jolly
-Poison Jab
-Protect
-Earthquake
-Swords Dance

---I would really like to keep Magcargo on my team since it is my favorite Pokemon. I use him a lot and I actually find him extremely useful. I've won numerous battles due to Magcargo. I am, however, open to suggestions.
---I would also like to keep Rotom on my team as well. I am willing to change his form to better fit the team though.
---I am willing to switch out the other four Pokemon for new ones if it makes my team better. I like using unique Pokemon (Pokemon that don't get used as much as others) but I am willing to use OU Pokemon as well.

 

[PlatinumDude]

Having more than 510 EVs is impossible, as seen with Tangrowth:
-Giga Drain/Leaf Storm
-Knock Off
-Earthquake
-Hidden Power (Ice/Fire)/Rock Slide
Nature: Relaxed
EVs: 252 HP/4 Def/252 SDef
Item: Assault Vest
Ability: Regenerator

or
-Giga Drain
-Knock Off
-Sleep Powder/Earthquake
-Hidden Power (Ice/Fire)
Nature: Relaxed
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Regenerator

Focus Blast is a necessity to deal with Ferrothorn and Excadrill if Mega Ampharos is to be on the offensive. Also, what purpose does your current EV spread serve? RestTalk is viable on Mega Ampharos; though it'll be walled by the Pokemon I mentioned. RestTalk Mega Amphy is an offensive pivot:
-Rest
-Sleep Talk
-Volt Switch
-Dragon Pulse
Nature: Modest
EVs: 252 HP/44 SAtk/192 SDef/20 Spe (2HKOs Hippowdon with Dragon Pulse while outspeeding it at the same time)
Item: Ampharosite
Ability: Static

or
-Volt Switch
-Dragon Pulse
-Focus Blast
-Thunderbolt/Heal Bell
Nature: Modest
EVs: 236 HP/252 SAtk/20 Spe
Item: Ampharosite
Ability: Static

Honestly, I don't like having Magcargo in an OU team. Its common weaknesses to Water, Fighting and Ground do it no favors, as those types of attacks are all over the place. Shell Smash + Recover is a big no-no; Magcargo won't have time to Recover off any damage it sustains if it Shell Smashes, plus it takes up a moveslot that would've gone to an extra coverage move. It's also too slow for Shell Smash in the first place (Torkoal may be slower than Magcargo, but it gets away with Shell Smash because it threatens the spin blockers in NU). As a result of this, Magcargo is better off using a defensive set, despite its bad defensive typing (at least it checks Talonflame):
-Stealth Rock
-Lava Plume
-Toxic
-Recover
Nature: Bold
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Flame Body

Given how Magcargo is vulnerable to all entry hazards, Rapid Spin or Defog support is a necessity:
Starmie:
-Hydro Pump/Surf
-Thunderbolt/Psyshock
-Ice Beam
-Rapid Spin
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Leftovers/Life Orb
Ability: Natural Cure

or
-Scald
-Rapid Spin
-Psyshock/Ice Beam/Thunderbolt
-Recover
Nature: Timid
EVs: 248 HP/32 Def/4 SAtk/224 Spe
Item: Leftovers
Ability: Natural Cure

Excadrill:
-Earthquake
-Rock Slide/Iron Head
-Rapid Spin
-Swords Dance/Stealth Rock
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Air Balloon/Chople Berry
Ability: Mold Breaker

or
-Swords Dance
-Earthquake
-Rapid Spin
-Rock Slide/Substitute/Iron Head
Nature: Adamant
EVs: 176 HP/60 Atk/252 SDef/20 Spe
Item: Leftovers
Ability: Mold Breaker

Mandibuzz:
-Foul Play
-Roost
-Taunt/Whirlwind
-Defog/Toxic/Knock Off
Nature: Bold/Impish
EVs: 248 HP/216 Def/44 SDef
Item: Leftovers
Ability: Overcoat

Crobat:
-Brave Bird
-Defog
-Roost
-Taunt/Toxic
Nature: Jolly
EVs: 168 HP/136 Atk/4 SDef/200 Spe
Item: Black Sludge
Ability: Infiltrator

Scizor:
-U-turn
-Bullet Punch/Knock Off
-Defog
-Roost
Nature: Impish
EVs: 248 HP/252 Def/8 SDef
Item: Leftovers
Ability: Technician

Tentacruel:
-Scald
-Sludge Bomb
-Rapid Spin
-Knock Off/Toxic
Nature: Bold
EVs: 252 HP/224 Def/32 Spe
Item: Black Sludge
Ability: Liquid Ooze

 

[ShinyMagcargo]

My bad about the EV total with Tangrowth. It was a typo. I meant 4 spDef. I'll edit that. Also thanks for the advice. I'll definitely go with a defensive magcargo with recover, Toxic, and Lava Plume. I'll probably switch Ancientpower to Rock Slide and I don't have access to stealth rock on Magcargo yet. As for my EV spread on Ampharos, I was trying something different. It has worked out for me so far but if it presents a problem in the future, I'll change it. I've got a Crobat with Defog that I may use as well as a tentacruel, but I'll have to breed another with rapid spin. Thanks for the Advice.