You have no maximum hand size. At the beginning of your upkeep, if you have exactly thirteen cards in your hand, you win the game. {3}{U}: Draw a card.
She's always willing to lend a hand. It just won't be her own.
2021-09-24
Triskaidekaphile's triggered ability will trigger only if you have exactly thirteen cards in your hand as your upkeep starts. If you have fewer cards in your hand, you won't be able to draw cards during your upkeep in time to cause the ability to trigger.