Diamond Knight
Artifact Creature — Knight
Vigilance (Attacking doesn't cause this creature to tap.)
As this creature enters, choose a color.
Whenever you cast a spell of the chosen color, put a +1/+1 counter on this creature.
Alayna Danner
Core Set 2020 (M20)
• #224Rulings
You must choose one of the five colors of Magic as Diamond Knight asks you to choose a color. You can’t choose “artifact,” “colorless,” or “chartreuse.”
(wotc • 2019-07-12)
Diamond Knight’s ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
(wotc • 2019-07-12)
If you somehow control a Diamond Knight for which no color was chosen, its last ability will never trigger.
(wotc • 2019-07-12)
Rulings
You must choose one of the five colors of Magic as Diamond Knight asks you to choose a color. You can’t choose “artifact,” “colorless,” or “chartreuse.”
(wotc • 2019-07-12)
Diamond Knight’s ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
(wotc • 2019-07-12)
If you somehow control a Diamond Knight for which no color was chosen, its last ability will never trigger.
(wotc • 2019-07-12)