Viennar, God of Diplomacy

At the beginning of your upkeep, if you added
mana to at least one opponent's mana pool,
you get an experience counter.
Indestructible, defender, shroud
{g}, {t}: Add {x} to target player's mana pool,
where X is the number of experience counters
you have plus one.
{w/u}{w/u}: Untap Viennar.