Choose a Background, Friends Forever, and Doctors Companion I am grouping these next three together
See section 5, Turn Structure. 2
Shadowless cards were printed during the initial run of Base Set before the drop shadow was added to the card border in subsequent print runs, making them identifiable by their slightly different border design and, most importantly, the absence of the shadow that gives the variant its name
While the front halves of these cards are fine, the reward for flashing them back is great enough that they see play despite their front halves (although this sometimes requires a specific deck or synergy, like Madness for Roar of the Wurm or Gifts Ungiven for Unburial Rites)
but Atraxa is just a goodstuff Commander through and through
BPhillipYork: This enables a whole deck around discarding and replaying, essentially giving madness to everything in your deck, though, obviously it's mayhem