Social Pyramid Scheme

You get a bonus for inviting your friends and then they have to invite their friends.

Some games will give you a bonus when you invite your friends to play and link to them to your account. This bonus may be a one-time benefit, or it may be an ongoing benefit that improves the gaming experience for each friend that you add. This gives players a strong incentive to convince their friends to play. Those friends then have to sign up more friends and so on, leading to a pyramid scheme and viral growth for the game.

Often, this is combined with another Dark Pattern called Social Obligation where you and your friends can help each other in the game. This leads to a feeling of obligation and people keep playing the game even when they no longer enjoy it.


Examples

UNO!™ UNO!™
"The game really, really wants you to connect the game to your Facebook account (presumably to get to your contacts). Others have reported that it's impossible to change your username or use a custom Pfp w/out doing so."

PK XD PK XD
"It does, if you invite you get newer items."

Knotwords Knotwords
""Share this puzzle" to encourage others to play, but no way to get them to a specific puzzle even if they pay to play"

AFK Arena AFK Arena
"You can borrow a hero once (3 times on certain subscription) to get through a difficult fight one time in campaigns nd one time in tower and infinite times in two day battles and some permanent content."

Words of Wonders: Crossword to Connect Vocabulary Words of Wonders: Crossword to Connect Vocabulary
"I think you get gems for inviting friends but I never bothered doing it because gems are easy enough to get just by playing occasionally lol"

Immortal Taoists-Idle Game of Immortal Cultivation Immortal Taoists-Idle Game of Immortal Cultivation
"You get free resources for sending invites to your friends"

Pikmin Bloom Pikmin Bloom
"You can now earn rewards by referring friends to play."

MY LITTLE PONY: MAGIC PRINCESS MY LITTLE PONY: MAGIC PRINCESS
"Being a mentor allows you 10 gems when your mentored (you can choose one mentor and can enter them only until you're level 10) reach levels 10, 25, 50 and 100. You can send them notifications to remind them to play"

Identity V Identity V
"two incentives to invite other players. first: like other games, you get in-game rewards for inviting friends. second: if you play as survivor w/ a team of friends & speaking over voice chat/in person, you have a better advantage in winning than survivors who are playing alone."

FarmVille 2: Country Escape FarmVille 2: Country Escape
"Some quests ask you to link your facebook or invite other friends who play the game to your "co-op" for rewards."