[@Cyclone][@Legion02]

I don't agree with Legion's summary of it being 'in-domain [i]but extreme[/i]'. The Spark is, arguably, borderline out-of-domain due to the fate-manipulation aspect. I'd recommend either removing the challenge-creation mechanism or reworking it, if you want it to be still 2 Conviction. 

If you want to keep it as is, however, I would say it deserves to be upgraded to [color=red][b]Nightmare [/b][/color]tier because it's introducing a fundamental reality-altering system (fate/challenge-scaling) that affects how events unfold. [color=red][b]Nightmare [/b][/color]tier is for "actions that fundamentally alter reality's rules or introduce cosmic-scale threats. (Which in this case would be 3 Conviction and 100% Turbulence)

If you leave it as is, I would also allow it to affect all sapients currently in existence, since it would be a significant enough action to warrant this. If you leave it as [color=orange][b]Surreal[/b][/color] (after removing the fate stuff) it will only affect latter descendants and not current humans.

The talent/obsession/transformation parts are fine—it's specifically the "subtle forces made by the larger Spark blessing" that crosses into territory Excelsis hasn't established authority over just yet.