Twenty-Toed Toad

Your maximum hand size is twenty.
Whenever you attack with two or more creatures, put a +1/+1 counter on Twenty-Toed Toad and draw a card.
Whenever Twenty-Toed Toad attacks, you win the game if there are twenty or more counters on it or you have twenty or more cards in hand.

The List

Bloomburrow Commander

If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Twenty-Toed Toad onto the battlefield and then put Spellbook (an artifact that says you have no maximum hand size) onto the battlefield, you would have no maximum hand size. However, if those permanents entered in the opposite order, your maximum hand size would he twenty.

Twenty-Toed Toad's last ability will trigger whenever it attacks, no matter how many counters are on it or cards you have in your hand at that time. The number of counters on it and the number of cards in your hand are only checked when that ability resolves.

Your maximum hand size is only checked during the cleanup step of your turn. At other times, you may have more cards in hand than your maximum hand size.