If its an effect, it happens during resolution
Main Phase, where the turn player can play the cards from their hands, activate effects, summon monsters
When you need to have an answer to anything thrown at you, the best way is to draw a lot of cards before then
Card Grading: Near Mint (NM) - Cards in Near Mint (NM) condition show minimal to no wear from shuffling, play or handling and can have a nearly unmarked surface, crisp corners and unblemished edges outside of a few minimal flaws
If you apply Pokey's third ability as a replacement effect to rolling a d20, other than the original effect that called for the d20 roll, all other game effects, including replacement effects and triggered abilities, recognize that you flipped a coin rather than rolled a d20
However, after a feeling that some sets were so flooded with serialized cards that they werent as special anymore, WotC changed tactics and moved to one featured card instead