Faclier, Agent Provacateur and Mickey Mouse, Wayward Sorcerer in your hand, respectively
#15 WotC themselves draw a distinction between 'design' and 'development', where design is making cards and development is adapting those cards to the limited / standard environment
Azlask, the Swelling Scourge $19.50 Annihilator is a mechanic that, while generally balanced in the past, many players flat-out hate
In recent years, though, more Dragons have been printed at mana values that are priced to move
Theres also the Painter's Servant lock, where you set all spells to be the same color and now people cant play spells at all
There are 121 playtest cards in the set, and youll only find them in Convention Edition Mystery Boosters