(1/19/2018) You play the card as X's last ability resolves, with one exception: You can't play a land this way unless it's your turn and you have an available land play
As a sample, Ive gone 12-3 in my last 15 Magic Online two-man queues with this deck
So far, I'm roughly 300 packs (probably better known as $300 since packs cost $1 each) into Strixhaven on Magic Arena , after buying a 50-pack prerelease bundle, two 90-pack bundles, and a 45-pack bundle and opening some random packs that I bought with gold, earned as rewards, or got with the PLAYSTRIXHAVEN code
The creature half of Brazen Borrowers equally shrug-worthy
I ended up paying more in shipping and taxes to get this slab to me than the actual slab price itself
However, Sunstar Lightsmiths ability is extremely good