When Astral Dragon enters the battlefield, it and Molten Echoes trigger.
Resolve the Astral Dragon trigger, creating four token copies of Primal Vigor that are 3/3 Dragon creatures in addition to their other types.
Resolve the Molten Echoes trigger, creating a total of 32 Astral Dragon tokens with haste.
When the Astral Dragon tokens enter the battlefield, they trigger, creating an extremely large number of Primal Vigor tokens that are 3/3 Dragon creatures in addition to their other types.