Midnight Oil

This enchantment enters with seven hour counters on it.
At the beginning of your draw step, draw an additional card and remove two hour counters from this enchantment.
Your maximum hand size is equal to the number of hour counters on this enchantment.
Whenever you discard a card, you lose 1 life.

Kaladesh Remastered

Midnight Oil enters the battlefield with seven hour counters on it.
At the beginning of your draw step, draw an additional card and remove two hour counters from Midnight Oil.
Your maximum hand size is equal to the number of hour counters on Midnight Oil.
Whenever you discard a card, you lose 1 life.

Kaladesh Promos

Kaladesh

If Midnight Oil has no hour counters on it, its first triggered ability will continue to trigger and have you draw an additional card, even though you can't remove any counters from it.

If Midnight Oil has only one hour counter on it, its first triggered ability will remove that one counter.

If multiple effects try to set your maximum hand size to a certain number or state that you have no maximum hand size, the one created latest is the one that applies.

If you discard a card during your cleanup step while you control Midnight Oil, its last ability will trigger, and players will get priority in your cleanup step. You'll have another cleanup step after that one before continuing to the next player's turn.

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.