It uses a simplified model of the rules of Magic to perform a large number of playthroughs, each starting with a randomly shuffled deck, while recording whether were on or ahead of curve on each turn in each playthrough
It can take a few months, due to the process going to and from America and the high demand at present
The cost reduction for artifacts and creatures sacrificed earlier in the turn will apply even if you don't sacrifice any as an additional cost
Not only will players who spent $600 on a playset of Jace, the Mind Sculptor to play Modern be extremely mad (people get outraged over Standard bannings that might cost them $50I don't even want to imagine what happens when a somewhat large group of players finds out their $600 playset of Jace is rebanned and worth $100), but rebanning Jace, the Mind Sculptor would reinforce the idea that the unbanning wasn't about the health of Modern but purely a money grab designed to sell Masters 25 boosters
Regardless, it does have that appeal of being an Alolan version of one of the original Kanto 151, and this one appears in dragon form, meaning it has no weaknesses