Activate Earthcraft by tapping a creature, untapping a basic land you control.
Activate the basic land by tapping it, adding ({1} magic symbol) .
Activate Ruthless Knave's first ability by paying ({2} magic symbol) ({B} magic symbol) and sacrificing a creature, creating two Treasure tokens and two 1/1 Squirrel creature tokens.
Activate a Treasure token by tapping and sacrificing it, adding ({B} magic symbol) .
Activate Earthcraft by tapping a creature, untapping a basic land you control.
Activate the basic land by tapping it, adding ({1} magic symbol) .
Repeat.
Once you have infinite Treasure tokens, you may use them to activate Ruthless Knave's second ability.