Previous Versions can be found here.
Knife is a Determination Spell Card, added in Beta 6.6.
Although it is fairly cheap and can kill any enemy monster instantly, the player will lose HP equal to the Cost of the killed monster as result.
Best saved for rather cheap monsters with high ATK, HP or "DEF", such as Charles, Mettaton or Napstablook. It is worth mentioning using a Knife while having player invincibility, either from Frisk or Rouxls Kaard, will result in the DMG being negated, making it safe to be used on anything, including the expensive Legendary and Determination monsters.
Knife is also a vital part of a Snail DT Deck, which uses this alongside Loox and Vulkin to set yourself in a state to maximize the use of Last Dream. Combined with Snail Trainer to give Thundersnail and a proper setup with the Snails to make sure at least 2 Blue Snails are summoned from it to give your whole board Charge, you should be able to kill the opponent instantly (especially with 2 Last Dreams, as that gives you 4 monsters with at least 15 ATK that can attack right away).
- Red Knife (by Asrite)