It's supposed to tell you when you're allowed to play cards. There's a bit of a delay in which you can't play cards when you're playing another card, when the card draw animation is going on, and when your card effects are processing.
Elements 1.21
- A small green/red light appeared close to the cards in the hand. Players can not play more cards while the light is red, this will prevent several overlapping effects and bugs. When this happened in pvp it also caused desync.
Side effect: players have to wait for all the effects to be resolved.
