If you apply Pokey’s second ability as a replacement effect to flipping a coin, other than the original effect that called for the coin flip, all other game effects, including replacement effects and triggered abilities, recognize that you rolled a d20 rather than flipped a coin. For example, you can then apply the replacement effect of Pixie Guide but not the replacement effect of Krark’s Thumb. And after the roll, the ability of Brazen Dwarf would trigger, while the first ability of Tavern Scoundrel would not trigger.