You draw a card and discard a card all while Riddlesmith's ability is resolving. Nothing can happen between the two, and no player may choose to take actions.
07-08-2020
wotc
An ability that triggers when a player casts a spell resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.