If there's a legendary creature you'd like me to tackle, please let me know
In a typical set, you will open a specific mythic from 1 in 121 packs, while in Rivals of Ixalan , this number drops to 1 in 141 (basically, instead of opening a mythic from one in every eight packs like usual, it will be one in every nine packs in Rivals of Ixalan )
Jace Beleren isn't an assured card draw per turn like the previous cards, but we will mostly be using it's plus ability, so I count him among our steady card draw engine
Some players also use it in frog decks for flavor reasons, even though Sab-Sunen doesnt have the frog creature type
It shuts down other effects as well - your opponents can't cast spells from anywhere other than their hands, so no casting spells using Madness, Plot, Mayhem, or a whole bunch of red impulse draw effects