Wizkids Rules!

Character dice in your Reserve Pool gain Intimidate (until end of turn).

Does this only effect character dice in the reserve pool when the action is used? Or, will it give also give Intimidate to characters that enter the reserve pool after Yellow Lantern Ring is used?

Any Character dice that enter the Reserve Pool after Yellow Lantern Ring action die is used would not gain Intimidate. Yellow Lantern Ring’s ability is not persistent. When it is used, it checks the game state (i.e. dice that are in the Reserve Pool), applies its ability appropriately and is resolved.