The Royal Scions

[+1]: Draw a card, then discard a card.
[+1]: Target creature gets +2/+0 and gains first strike and trample until end of turn.
[−8]: Draw four cards. When you do, The Royal Scions deals damage to any target equal to the number of cards in your hand.

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If replacement effects cause you to draw five or more cards while resolving the last ability of The Royal Scions, its reflexive triggered ability still triggers only once, even if you draw eight cards.

If you draw fewer than four cards while resolving the last ability of The Royal Scions, its reflexive triggered ability doesn't trigger.

The Royal Scions's last ability goes on the stack without a target. While that ability is resolving, you draw four cards. When you do, the reflexive triggered ability triggers and you pick a target to be dealt damage. This is different from effects that say “If you do . . .” in that you choose a target after looking at the cards you draw.

You draw a card and discard a card all while The Royal Scions's first ability is resolving. Nothing can happen between the two, and no player may choose to take actions.