If a creature card in your graveyard has in its mana cost, X is 0.

Experience counters are the second kind of counters a player can have, joining poison.

Each game pack includes a card labeled “Experience” with the suggestion “Place your experience counters here.” This card isn’t required for play. It’s simply a convenient spot to put your experience counters, which can be represented with dice, glass beads, or other small items.

If Meren of Clan Nel Toth leaves the battlefield at the same time as other creatures you control die, its first ability will trigger for each of those creatures.

You can’t choose to put the creature card into your hand if its mana value is less than or equal to the number of experience counters you have as the ability resolves.

All experience counters are identical, no matter how you got them. For example, the last ability will count experience counters that you got from the first ability, from another ability, from proliferating, and so on.