This is not only a /+1 dice for tarmogoyf, this is a dice that hold all the possible state of tarmogoyf during play.
It has 8 side from 0/1 to 7/8
"The card types are artifact, creature, enchantment, instant, land, planeswalker, sorcery, and tribal"
So is possible that tarmogoyf can grow up to 8/9 but for my usage I'm more confortable having 0/1 instead of 8/9
But I plan to build also a dice that has 9 face if possible!