Each + loyalty symbol in Comet's abilities means to put the indicated number of loyalty counters on him. Each – loyalty symbol in Comet's abilities means to remove the indicated number of loyalty counters from him. The only difference is Comet uses these symbols in the effects of his abilities rather than the costs. Good boy, Comet.
Something in the game must tell you to roll a die. If you roll a die for any other reason (to simulate a coin flip, to choose pizza toppings, to create alternate timelines), that roll doesn't count.
In some unusual cases, Comet may gain loyalty abilities other than the one he normally has. In those cases, the effect of rolling a 6 applies only to his normal ability.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Jeff Miracola
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Each die is identified by the number of faces it has. A six-sided die is a die with six equally likely outcomes: 1, 2, 3, 4, 5, and 6. The roll must be fair. Although physical dice are recommended, digital substitutes are allowed except in cases where the physical die is required for the effect.
If you roll a 3 but there aren't any cards with mana value 2 or less in your graveyard, you'll just remove one loyalty counter from Comet. Sorry, boy.
If a die is rerolled, the original roll essentially never happened: it doesn't cause any abilities to trigger, and no effect that cares about die rolls will consider it.
None of Comet's abilities require a target. All choices for cards, creatures, or players are made as the abilities resolve.
If an ability triggers "whenever you roll a die," it will trigger whenever you roll any die, including the planar die. This is a change from previous Un- rules. Some abilities use the result to determine part of the effect. If you get a non-numerical result (currently just the planar die, but the future is long), that part of the effect won't do anything.
Results can be numbers not ordinarily possible on a six-sided die. Spells like Scooch can change the result to 0 or 7, for example.
Some effects may modify the result of a die roll. This may be part of the instruction to roll a die, or it may come from other cards. Anything that references the "result" of a die roll is looking for the result after these modifications.
If you roll a 4 or 5 while Comet has one loyalty counter on him, Comet will deal 1 damage to a creature or player and then that loyalty counter will be removed. Comet will then go live on a farm, where he'll be very happy but will miss you terribly.
