>>58424816
>>58421505
It also explains why the ultimate weapon was able to BOTH kill two entire armies and also revive the dead and give two beings unconditional immortality.
Two different legendaries, two different modes.
Plus, Lysandre wanting to hit the protag and their friends with immortality when we steal the battery instead of blow himself and everyone else to kingdom come just doesn't make much sense.
So the actual plan would be kill the world and make themselves into its immortal masters.
then when the protag steals the main battery (Xerneas), Lysandre tries to use the destructive potential (Yvetal) of what power is left to self-destruct in a ploy of spiteful mutually assured destruction, ultimately failing but destroying the base and leaving the weapon permanently inoperable.