That could be Swiftfoot Boots, but also consider Rising of the Day or Urabrask the Hidden
Also in Hour of Devastation Limited Vizier of the Anointed was an engine card that synergized incredibly well with various Blue and mainly White Embalm and Eternalize creatures
Id add the Ravnica Signets cycle here as well, but with Signets you often lose tempo the turn they enter
2 Trainer was awarded to winners at the 2006 Pokmon World Championship, and according to experts, only three of these were ever handed out
4 Teysa Of The Ghost Council Blink And Miss It Cards that can snowball are must-answer threats, and Teysa Of The Ghost Council is that, and it has to be answered on your turn since it'll exile itself at every end step
Loot has three different Exhaust uses, all tied to its color identity - the Green one adds three mana of any one color to a player's pool, the Blue one allows the owner to draw three cards, and the Red one deals three damage to any target
