2022-10-07 : Celestine’s triggered ability looks at the total amount of life you gained to determine X, regardless of whether or not you also lost any life. For example, if you gained 3 life this turn, X is 3, even if you also lost some amount of life in the same turn.

2022-10-07 : The target creature card is chosen as the triggered ability is put on the stack. Gaining life after that point won’t let you choose a target with a higher mana value.