This could be a Selvala, Heart of the Wild in a powers matter deck
A card with Challenger +1 would get 1 extra strength, but only while challenging not will being challenged, or at any other point in the game
They'd get a creature on the spot, and the threat to make more, forcing their opponent to come up with two answers rather than one
For example, a player can't activate the transmute ability of Muddle the Mixture if Pithing Needle naming Muddle the Mixture is on the battlefield
Something awful happened on that day
Paradox Engine: Speaking of the value express, Paradox Engine gets us the team untapped for defense, but perhaps a little extra mana in the form of the few mana rocks weve put into the deck