Hey LzzzR I was your Secret Santa and I got the Regigigas + Gourgeist team you requested. It took a lot of testing so I hope it doesn't disappoint!
Gourgeist-Super @ Colbur Berry
Ability: Frisk
EVs: 252 HP / 252 Def / 4 Spe
Bold Nature
IVs: 0 Atk
- Leech Seed
- Foul Play
- Will-O-Wisp
- Synthesis
Regigigas @ Leftovers
Ability: Slow Start
EVs: 252 HP / 252 Atk / 4 Spe
Adamant Nature
- Thunder Wave
- Substitute
- Knock Off
- Return
Pyukumuku @ Leftovers
Ability: Unaware
EVs: 252 HP / 4 Def / 252 SpD
Calm Nature
IVs: 0 Atk
- Block
- Recover
- Toxic
- Soak
Liepard @ Leftovers
Ability: Prankster
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Encore
- Copycat
- Substitute
- Knock Off
Silvally-Ghost @ Ghost Memory
Ability: RKS System
EVs: 252 HP / 252 Def / 4 Spe
Bold Nature
IVs: 0 Atk
- Parting Shot
- Shadow Ball
- Defog
- Thunder Wave
Audino @ Leftovers
Ability: Regenerator
EVs: 252 HP / 252 SpD / 4 Def
Careful Nature
IVs: 0 Atk
- Wish
- Protect
- Heal Bell
- Toxic
Ability: Frisk
EVs: 252 HP / 252 Def / 4 Spe
Bold Nature
IVs: 0 Atk
- Leech Seed
- Foul Play
- Will-O-Wisp
- Synthesis
Regigigas @ Leftovers
Ability: Slow Start
EVs: 252 HP / 252 Atk / 4 Spe
Adamant Nature
- Thunder Wave
- Substitute
- Knock Off
- Return
Pyukumuku @ Leftovers
Ability: Unaware
EVs: 252 HP / 4 Def / 252 SpD
Calm Nature
IVs: 0 Atk
- Block
- Recover
- Toxic
- Soak
Liepard @ Leftovers
Ability: Prankster
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Encore
- Copycat
- Substitute
- Knock Off
Silvally-Ghost @ Ghost Memory
Ability: RKS System
EVs: 252 HP / 252 Def / 4 Spe
Bold Nature
IVs: 0 Atk
- Parting Shot
- Shadow Ball
- Defog
- Thunder Wave
Audino @ Leftovers
Ability: Regenerator
EVs: 252 HP / 252 SpD / 4 Def
Careful Nature
IVs: 0 Atk
- Wish
- Protect
- Heal Bell
- Toxic
This was a fairly difficult team to make, but I feel like it actually turned out pretty well. Anyways, its a stall team thats built around weakening the opposing team to support a late game Regigigas sweep (Something that occurs way more often then I first thought). The first mon on the team is Gourgeist, and it works pretty well with Audino to form the defensive backbone of the team. They both help compliment each others strengths and weaknesses and can pretty easily spread status throughout the whole game. Miltank actually forms a better core with Gourgeist (due to thick fat), but I felt like wish support is pretty necessary on this team, so I went with my gut and added Audino. Audino gives some nice wish passes and it can also pull of some clutch heal bells. Regigigas and Silvally in particular really enjoy the support that Audino gives, as it keeps them alive and status-free for much longer. The next mon, Pyukumuku, is also pretty important to the team. A surprising number of people underestimate it and don't realize that it can get block, only thinking it can use soak and toxic. These three moves work incredibly well with each other and can wear down a lot of mons (Ferroseed and Skuntank immediately come to mind). After you block them in, go for soak even if they can be toxiced first. Removing their STAB is usually more important then getting a few extra toxic turns. Pyukumuku really shines versus physical sweepers like Carracosta and Gurdurr, as it ignores their stat boosts via unaware. Just be really careful not to let opposing mons get up a substitute, because that can be really problematic for Pyukumuku and the rest of the team. The next mon on the team is Silvally-Ghost. Its fairly bulky, but can get worn down after a while. Just make sure to keep it healthy via Audino's wish passing and heal bells. Parting shot is really helpful and provides a ton of momentum. Using thunderwave, then parting shot is a particularly nice combo that works really well with Regigigas, allowing it to take more hits and not waste turns on its own thunderwaves. Another good combo is to use parting shot on a predicted switch. Then you can go into Liepard and use copycat to get ANOTHER parting shot and even more momentum. Liepard itself is also a key member of the team. It stops defensive mons in their tracks, and can sometimes use their own moves against them with copycat. Something I like to do is to encore a mon into stealth rocks/spikes, then use copycat to give them their own hazards. Liepard can also encore mons into various setup moves then use copycat to use the setup moves for itself. The final and most important mon on this team is Regigigas, which the whole team was centered around. Max HP can make it really bulky, and max attack makes it hit like a truck when slow start wears off. Knock off and return hit a lot of mons and help Regigigas hit Type: Null and other eviolite users. Silvally's parting shot helps gigas take even more hits, and Audino's wish/heal bell allow it to become a threat even after it had formerly been crippled. However, there are a few notable weaknesses to the team that I discovered when testing it. The first of these weaknesses is that nothing can switch in on a toxic, or absorb toxic spikes, which can sometimes be annoying. The other weakness is substitute, which can make some of your mons useless. Other then that, it plays surprisingly well, and can dish out some real punishment. I hope you enjoy the team; although it isn't top ladder good, it can certainly hold its own.