Foretell is a new mechanic in Kaldheim that lets you put cards on the battlefield before actually playing them. This is clearly a control-themed mechanic, which gives players a lot of flexibility and new possibilities for reactive plays besides typical instant spells.
Cosmos Charger can easily become the axis of any Foretell deck in standard due to its cost reduction ability. You can also use this ability on your opponent's turn, which gives you even more flexibility.
This mechanic is excellent for hiding your intentions from your opponents, especially if they use hand-revealing spells. They won't have access to the Foretell cards in the exile, and thus will have no idea what is it that you're preparing to play.