弩(ど)弓(きゅう)隊(たい)の熱(ねっ)狂(きょう)者(しゃ)

Modified creatures you control have menace. (Equipment, Auras you control, and counters are modifications.)

When Artillery Enthusiast enters the battlefield, you may discard a card. If you do, seek a card with mana value equal to that card's mana value. (To seek a card, put one at random from your library into your hand.)