Jolrael, Mwonvuli Recluse

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.

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.