Blood Lust

Instant, 1R (2)
If target creature has toughness 5 or greater, it gets +4/-4 until end of turn. Otherwise, it gets +4/-X until end of turn, where X is its toughness minus 1.¹
Illus. Anson Maddocks

Gatherer Card Rulings [Nov 2009]

• 11/1/2005: Has changed slightly in functionality, with the old continuous nature of the toughness reduction gone away; the toughness change remains static.  For example, if you have three Swamps and Nightmare on the battlefield and then cast Blood Lust on it, it will become 7/1.  If one of your Swamps is subsequently destroyed, your Nightmare will become 6/0 and be put in the graveyard.

Format Legality	Legal in Vintage, Legacy Banned in Extended, Standard, MTGO Classic
Printings (4/19)	Fifth Edition (Common) Fourth Edition (Common) Legends (Uncommon (U1)) MTGO Masters Edition III (Common)