I would like some advice on what Pokemon to put on my team for this tournament, other than the Super-Size Gourgeist as that's required, I'm thinking of using the event Gengar that'll be coming out, a Golurk with No Guard, Aegislash, Sableye, and Shedinja.
No Guard Golurk isn't that useful, since all the participants are immune to Dynamic Punch. You could boost Stone Edge to 100% accuracy, though Chandelure is already hit hard by Earthquake, while everyone else falls to Iron Fist Shadow Punch. Iron Fist is still the way to go to make Shadow Punch a usable attack:
-Rock Polish
-Earthquake
-Shadow Punch
-(filler)
Nature: Adamant/Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Lum Berry
Ability: Iron Fist
Obviously, Super Size Gourgeist is a must:
-Will-o-Wisp
-Leech Seed
-Seed Bomb
-Shadow Sneak/Phantom Force/Protect
Nature: Impish
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers/Sitrus Berry
Ability: Frisk
or
-Phantom Force
-Seed Bomb/Bullet Seed
-Shadow Sneak
-Will-o-Wisp
Nature: Adamant
EVs: 252 HP/252 Atk/4 Def
Item: Leftovers/Kasib Berry
Ability: Frisk
Take note of Aegislash's versatility:
-Shadow Ball
-Shadow Sneak/Iron Head
-Iron Head/Pursuit
-King's Shield
Nature: Quiet
EVs: 244 HP/12 Def/252 SAtk
Item: Leftovers/Weakness Policy/Spooky Plate/Spell Tag
or
-Substitute
-Toxic
-King's Shield
-Shadow Ball
Nature: Modest
EVs: 244 HP/12 Def/252 SAtk
Item: Leftovers
or
-Shadow Ball
-Shadow Sneak
-Flash Cannon
-Pursuit
Nature: Hasty/Naive
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb
or
-Swords Dance
-Shadow Sneak
-Iron Head/Shadow Claw
-Head Smash/Shadow Claw
Nature: Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb
You don't really need the event Gengar; any Gengar you can get yourself does fine. IMO, shiny Gengar doesn't look too different from regular Gengar. But if you're thinking of using Mega Gengar in this, don't. Unless you want the extra Speed, Mega Gengar isn't worth it because Shadow Tag is useless against Ghosts, since they're immune to trapping moves/abilities. You're better off using regular Gengar in that case:
-Shadow Ball
-Sludge Bomb/Sludge Wave
-Focus Blast
-Destiny Bond
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb
or
-Substitute
-Shadow Ball
-Will-o-Wisp
-Disable/Taunt/Sludge Bomb/Sludge Wave/Focus Blast
Nature: Timid
EVs: 28 HP/148 SAtk/80 SDef/252 Spe
Item: Black Sludge
or
-Hex
-Substitute
-Will-o-Wisp
-Taunt
Nature: Timid
EVs: 144 HP/108 SAtk/4 SDef/252 Spe
Item: Black Sludge
Sableye should abuse Prankster to the fullest:
-Taunt
-Will-o-Wisp
-Recover
-Foul Play/Knock Off
Nature: Bold/Impish
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers/Sitrus Berry
Ability: Prankster
Before you even think of using Shedinja, don't. Take note that Wonder Guard makes it only vulnerable to super effective hits. Consider that this Friendly is for Ghost Pokemon only. Put 2 and 2 together, and this means that Shedinja gets totally screwed in this Friendly.