There have been a couple of different Lapras Teams ever since its Gigantamax Form was Released in series 3.I'll go through and list teammates/movesets/strategies for each. The standard lapras set will be Shell Armor, protect/thunder/hydro pump/freeze dry or blizzard, depending on the team, but EVs will vary.
Bulky Lapras + Comfey
Probably the most popular form was/is Lapras/Comfey/Sap Sipper (Usually Goodra, but I like Bouffalant) with Giga Drain for weakness policy. Usually Lapras will be max attack, max hp, minimum speed and Comfey will carry trick room since it's pretty slow. I personally really like this team composition, it carried me really high on the ladder. This was in series five, I ran Comfey/Bouffalant/Crit Togekiss/Cinderace/Rillaboom. Bouffalant benefits from trick room and gig drain, and the rest of the team was hyper offense. The idea is to set trick room, aurora veil and weakness policy, and by the time comfey goes down, you'll either have priority or trick room will be over for your sweepers. Cinderace in the back was fantastic in Aurora veil, it could live attacks it could never before. Pretty much all frail sweepers benefit from aurora veil, especially if you can navigate trick room to end before aurora veil.
Lapras-Gmax @ Weakness Policy
Ability: Shell Armor
Level: 50
EVs: 252 HP / 252 SpA / 4 SpD
Quiet Nature
IVs: 0 Atk / 0 Spe
- Protect
- Thunder
- Freeze-Dry
- Hydro Pump
Comfey @ Focus Sash
Ability: Triage
Level: 50
EVs: 252 HP / 4 Def / 252 SpD
Calm Nature
IVs: 0 Atk
- Protect
- Trick Room
- Floral Healing
- Giga Drain
Goodra @ Assault Vest
Ability: Sap Sipper
Level: 50
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
(Moves/Item are your choice, whatever fits your team)
- Outrage
- Iron Tail
- Fire Punch
- Stomping Tantrum
Note: Before comfey was here, Dusclops was used with essentially the same role. You can run brick break to reset screens or rock tomb to lower speed in the face of Pokemon like Rhyperior.
Dusclops @ Eviolite
Ability: Frisk
Level: 50
EVs: 252 HP / 252 SpD
Sassy Nature
IVs: 0 Atk / 0 Spe
- Night Shade
- Trick Room
- Pain Split
- Rock Tomb
Tailwind + Fake Tears
Another team that was gaining popularity in series 5 was Hyper offensive Lapras plus Whimsicott. Lapras was max attack max speed modest with either life orb or light clay and whimsicott always carried fake tears and tailwind. This was strong because Lapras is already bulky with Dynamax and aurora veil, plus it frees up the item slot because fake tears is basically a temporary weakness policy. Since whimsicott is gone, people still use Talonflame but it doesn't have the same damage output. The only Pokemon with Tailwind + Fake tears now is Mandibuzz, which could be interesting (overcoat + taunt is very strong) but it really misses priority tailwind. Pokemon that benefit from this are, again, Frail sweepers, as Aurora veil helps them immensely and they can be further powered up with tailwind and possibly fake tears. Bulky togekiss could be strong with tailwind/Fake tears support as well, in my opinion. Usually this lapras will run Blizzard for the extra power without fake tears support, especially on a talonflame team.
Lapras-Gmax @ Life Orb
Ability: Shell Armor
Level: 50
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Protect
- Blizzard
- Thunder
- Hydro Pump
Talonflame @ Safety Goggles
Ability: Gale Wings
Level: 50
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Tailwind
- Taunt
- Hurricane
- Protect
Mandibuzz (F) @ Focus Sash
Ability: Overcoat
Level: 50
EVs: 252 HP / 4 Def / 252 Spe
IVs: 0 Atk
- Tailwind
- Taunt
- Fake Tears
- Foul Play
Whimsicott @ Focus Sash
Ability: Prankster
Level: 50
EVs: 252 HP / 252 Spe
Timid Nature
IVs: 0 Atk
- Protect
- Tailwind
- Fake Tears
- Moonblast
Decorate
Decorate Lapras Teams focus on setting aurora veil to become very bulky, using decorate with Alcremie to constantly to buff your stats, and being able to sit around, KOing your opponents before they can get rid of you. Safety goggles Alcremie is strong for this team, it also learns baby doll eyes to further increase bulk. Slow, specially bulky assault vest Duraludon is a good partner to this team as well, it can raise its defense with max steelspike while getting buffed by decorate. Typically, this Lapras will run light clay and a lot of bulk to stick around as long as possible.
Note: Wolfe Glick featured one of these teams here.
Lapras-Gmax @ Light Clay
Ability: Shell Armor
Level: 50
EVs: 252 HP / 252 SpA / 4 SpD
Quiet Nature
IVs: 0 Atk
- Protect
- Freeze-Dry
- Thunder
- Hydro Pump
Alcremie (F) @ Safety Goggles
Ability: Sweet Veil
Level: 50
EVs: 252 HP / 60 Def / 196 Spe
Bold Nature
IVs: 0 Atk
- Protect
Duraludon-Gmax @ Assault Vest
Ability: Stalwart
Level: 50
EVs: 100 HP / 4 Def / 92 SpA / 252 SpD / 60 Spe
Modest Nature
IVs: 0 Atk
- Flash Cannon
- Draco Meteor
- Thunderbolt
- Snarl
Pros and Cons of Lapras
Lapras is a very bulky and flexible Pokemon with a fantastic Gmax Move effect that can support the whole team and cause survivals and wins that could never have happened without screens. However, it is slow and weak offensively without both speed control and setup, making it easy to target down the support Pokemon. (It's REALLY easy to read a turn one lapras protect and double comfey.) Additionally, they have been widely regarded as "good" teams and therefore more prepared for and harder to navigate.
Hopefully this answers your questions!