All the monsters that were under Vinei's command were becoming Heaven Immortals. Millions and millions of them, each one nurturing their strength since time unknown. In fact, Vinei himself was undergoing a tribulation, although his was a little different.
He was not undergoing a tribulation to become a Heaven Immortal. Rather, he was bearing the universe's punishment for forsaking his role as a Deity!
Just like when diviners and oracles. who foresaw a future that they should not have seen or revealed, were punished through a tribulation, many others who earned the ire of the universe suffered as well. Using his divine fire to baptise his physical body to build himself the ultimate foundation for when he gave up divinity gave him a huge advantage. In fact, his entire journey to the very peak of the Celestial realm would be a piece of cake after this. But he also provoked the universe through his actions, and thus he earned a tribulation.
