Spymaster's Vault is a rare Land card from Modern Horizons 3 (MH3), collector number 358. Current market price: $3.83 (foil $7.71), TCGplayer market prices via Scryfall.
This land enters tapped unless you control a Swamp. {T}: Add {B}. {B}, {T}: Target creature you control connives X, where X is the number of creatures that died this turn. (Draw X cards, then discard X cards. Put a +1/+1 counter on that creature for each nonland card discarded this way.)