Blitzball Stadium is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

When this artifact enters, support X. (Put a +1/+1 counter on each of up to X target creatures.) Go for the Goal! — , : Until end of turn, target creature gains "Whenever this creature deals combat damage to a player, draw a card for each kind of counter on it" and it can't be blocked this turn.