Jolrael, Mwonvuli Recluse

Whenever you draw your second card each turn, create a 2/2 green Cat creature token.
{4}{G}{G}: Until end of turn, creatures you control have base power and toughness X/X, where X is the number of cards in your hand.

"Humans bring nothing but suffering and deceit. They are not welcome in my forest."

Bloomburrow Commander

Murders at Karlov Manor Commander

Commander Masters

Dominaria Remastered

Effects that modify an affected creature's power and/or toughness without setting them to specific values will apply no matter when those effects began. The same is true for counters that change the creature's power and/or toughness.

Jolrael's last ability overwrites all previous effects that set the affected creatures' power and/or toughness to specific values. If other effects that set these characteristics to specific values start to apply after Jolrael's ability resolves, they will overwrite that part of the effect.

The triggered ability can trigger only once each turn. It doesn't matter if Jolrael was on the battlefield when the first card was drawn: if it's not on the battlefield when the second card is drawn, the ability can't trigger at all that turn.

The value of X is determined only as Jolrael's last ability resolves. Once that happens, the value of X won't change later in the turn even if the number of cards in your hand changes.