Like most Magic: The Gathering cards, the value of Doomsday Excruciator depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Duskmourn: House of Horror)
A rare might give you a solid creature or a useful spell
Probably more for security purposes
There is a bit of deck building tech if you put in a number of historic lands, likely Legendary lands to mitigate getting stuck on lands
Some new legends take color combinations into exciting new territory, while others lean into what makes their color identity a blast to play
The art for Leatherhead, meanwhile, is a riff on the Wild West theme from the alligators SNES Turtles In Time appearance