The Slot bug refers to the Slot command in Final Fantasy VI. The Slot ability, Joker Doom, which will instantly kill the player's party, is capable of teaching Lv.5 Death to Strago if he has not learned it yet. The reason for this happening is due to Joker Doom being a modified Lv.5 Death that has the instant death protection removed and replaced with the unblockable property. This, however, is useless, as there is no way to prevent Joker Doom from killing the party and causing a Game Over.