When Coveted Jewel enters, draw three cards. : Add three mana of any one color.
Whenever one or more creatures an opponent controls attack you and aren’t blocked, that player draws three cards and gains control of Coveted Jewel. Untap it.
Coveted Jewel's last ability triggers after you declare blockers (or declare no blockers at all) if any attacking creatures are unblocked. It doesn't matter if some attacking creatures were blocked.
13-07-2018
wotc
A creature attacking a planeswalker you control won't cause Coveted Jewel's last ability to trigger.
13-07-2018
wotc
Coveted Jewel's last ability resolves after blockers are chosen but before combat damage is dealt.
13-07-2018
wotc
If more than one opponent attacks you at the same time, Coveted Jewel's last ability triggers for each of them. You choose which player ends up with Coveted Jewel, but each of them draws three cards and has a chance to activate its mana ability.
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.