Pair o' Dice Lost doesn't target any of the cards in the graveyard. You choose which cards you're returning to your hand, if any, after rolling the dice.

You can return any number of cards with mana value 0 (such as land cards) from your graveyard to your hand regardless of the results.

If Pair o' Dice Lost resolves, it will be exiled, even if you don't return any cards to your hand.

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 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.

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.

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 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.

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.