This page of the Ratchet & Clank Rift Apart game guide answers two important questions - whether multiplayer is available, and if you can play in co-op with another player. This can be important if, for example, you are looking for a good game to play with a friend.
As a reminder, Ratchet & Clank Rift Apart features as many as 5 different playable characters, though not all are equally relevant in terms of taking control of them. Typically, you follow the adventures of a select two characters - Ratchet with Clank/Kit or Rivet with Clank/Kit. We have listed all available heroes on a separate page titled Playable Characters.
Unfortunately, the authors of the game did not provide any multiplayer modes. Neither co-op nor online gameplay is available. Ratchet & Clank Rift Apart is an entirely single player experience. You will simply be switched to a particular character at precise moments in the story. However, you always control a single character and a possible second player sitting at the same console cannot help in any way, unfortunately.