Wall of Tombstones | Magic: The Gathering
Formats Wall of Tombstones is Legal in
Official Oracle Text for Wall of Tombstones
At the beginning of your upkeep, change Wall of Tombstones's base toughness to 1 plus the number of creature cards in your graveyard. (This effect lasts indefinitely.)
Official Rulings for Wall of Tombstones
10/1/2009 : The effect from the ability overwrites other effects that set power and/or toughness if and only if those effects existed before the ability resolved. It will not overwrite effects that modify power or toughness (whether from a static ability, counters, or a resolved spell or ability), nor will it overwrite effects that set power and toughness which come into existence after the ability resolves. Effects that switch the creature's power and toughness are always applied after any other power or toughness changing effects, including this one, regardless of the order in which they are created.