The guaranteed pull structure means every box delivers specific ultra-rare cards unlike regular booster boxes where you might get nothing above RR rarity
Direct damage, multiple targets Friendly to creatures Friendly to lands Increasing counters and/or tokens Playing cards off the top of your library, paying their mana cost (You may look at the top card of your library and if it's a [blah] you may play it.) Putting artifacts from hand onto the battlefield Return target creature from graveyard to hand
While we haven't seen any truly standout performances in Modern Challenges on MTGO just yet, the deck has performed excellently in Modern Leagues, with many players piloting Living End to a 5-0
We just got a fair chunk of WB Knight Tribal support in Dominaria led by Aryel, Knight of Windgrace, so it's strange that the very next set would throw some nice Knight Tribal support
Or, it could be an ongoing scheme, in which case it remains on the field until an ability causes you to abandon it