If Jackdaw Savior and another creature you control with flying die at the same time, Jackdaw Savior’s last ability triggers for each of them.

The target creature card must have a lesser mana value than the creature that caused Jackdaw Savior’s last ability to trigger. Use the mana value of that creature as it last existed on the battlefield to determine which creature cards in your graveyard are legal targets for that ability.

If a creature on the battlefield or a creature card in a graveyard has {X} in its mana cost, X is 0 for the purpose of determining its mana value.