There are lots of different Games that use Twitch as an interaction method between viewers and streamers. In this article there are 4 examples of this technique, sorted by complexity of integration.
Warhammer Vermintide 2
Gameplay: First-person coop shooter
Interaction: The twitch chat has certain operators to choose from with commands in the chat. They can ether give the player items that are helpful or spawn more and more enemies. Ether the make the gameplay easier or harder.
Gameplay: 2D platformer, roguelike inspired by Metroidvania-style games.
Interaction: „Captain Chicken“ -> one viewer can decide when to heal the streamer and send messages in game, visible for all viewers. Furthermore, the rest of the chat can vote for specific upgrades for the streamers character.
© Jeff Grubbs Game Mess on YouTube
One Troll Army
Gameplay: Tower Defense, with a playable character controllable like a MOBA Game.
Interaction: Everybody in the chat can join the game as an enemy character trying to destroy the camp of the streamer and defeat them. They have commands on the stream.
© TinyBuildGames on YouTube
Party Hard 2
Gameplay: Stealth 2D strategy game
Interaction: At the start of a round twitch viewers can create the environment in which the streamer has to navigate, they can place items, enemies etc. After a two minutes setup the player joins the room and try achieving certain challenges. There are also some special bonuses for the chat when the streamer dies due to them or are certainly helpful.
© tinyBuildGAMES on YouTube