The reward box a first-time party player-killer receives — containing only a booklet of betrayal PVP coupons.
A Savage Box is the reward the System grants the first member of a party to earn a player-killer skull. Rather than loot, it contains only a booklet of PVP Coupons — one for each party member. Both Princess Donut (after killing a crawler at Club Vanquisher) and Imani (on the first floor) received one and quietly disposed of the coupons inside; a Gold Savage Box is itself among the lavish rewards for actually redeeming a coupon.
Carl pieces the mechanic together while investigating the coupon Katia Grim recovered, understanding the box exists to seed betrayal within teams.
A reward box (undescribed) whose only contents are a booklet of skull-embossed betrayal coupons.
The delivery mechanism for the party-poisoning PVP coupon booklet.
Also appears in books you've already read — spoiler-safe to their endings: