As per August 12, 2024 Cult of the Lamb has blessed us with a free update bringing a 2-player co-op mode and more new gameplay features like new buildings, traits, relics and tarots.
With this, you may now not only join your holy lamb friend as The Goat and play through the entire campaign together but also go fishing together or share cult chores.
For best results the devs do recommend you use a local co-op mode (both players playing on the same machine), but Steam Remote Play is also supported if you can't play together locally. For best results, at least one player should be using a controller (player 2 may both either)