[Biesmen]

You're setting someone's HP to -20, which is lower than 0, which means you're dead.

Correct usage:

pawn Код:

new Float:hp;

GetPlayerHealth(pID, hp);
SetPlayerHealth(pID, hp -20);

for your /slapall command:

pawn Код:

new Float:hp;

GetPlayerHealth(i, hp);
SetPlayerHealth(i, hp -20);