Tishana, Voice of Thunder

Tishana's power and toughness are each equal to the number of cards in your hand.
You have no maximum hand size.
When Tishana enters, draw a card for each creature you control.

The Lost Caverns of Ixalan Commander

Tishana, Voice of Thunder's power and toughness are each equal to the number of cards in your hand.
You have no maximum hand size.
When Tishana enters the battlefield, draw a card for each creature you control.

Ixalan

Ixalan Promos

Because damage remains marked on a creature until it's removed as the turn ends, the damage Tishana takes during combat may become lethal if cards leave your hand later in the turn, such as by casting them in your postcombat main phase.

If Tishana enters the battlefield while you have no cards in hand, it will be put into your graveyard for having 0 toughness before its triggered ability resolves.

The number of creatures you control is counted only as Tishana's last ability resolves. If Tishana is still on the battlefield, it'll count itself.