I think it was there before, during that vacation time.
"Welcome home." Kamila kissed him softly after Lith reassured Aran that they would go to the Blackest Day together.
Fantasy · Legion20
So you can get tribulations even after white core? I guese that explains Faluel's story of Guardians dying. Failing a tribulation could be one way.
"Because an Awakened being able to reject a world tribulation before the white core is a rare event. The world energy in Kolga is thin, but not so much to hinder Mogar's vision or its influence.
Fantasy · Legion20
I think only a white core would be able to kill another that quickly. Anyone below that even in a large group would probably need a lot of time to get past their top of the line items or mage towers. It's also possible that Mogar protects them since it forces them to watch.
The only change was that all Guardians and all white-cored beings on Mogar had their consciousness forced to bear witness of the events, no matter what they had been doing.
Supreme Magus
Fantasy · Legion20