//Coloque no OnPlayerCommandText:

if(!strcmp(cmdtext, "/kill", true))
    {
        KillTimer(GetPVarInt(playerid, "TimerKill"));
        new Timer;
        SendClientMessage(playerid, 0x33CCFFAA, "Espere 5 segundos para morrer !");
        Timer = SetTimerEx("Matar", 5000, false, "n", playerid);
        SetPVarInt(playerid, "TimerKill", Timer);
        return 1;
    }


//E, no Final do GM:

forward Matar(playerid);
public Matar(playerid)
{
    SendClientMessage(playerid, 0xFF0000FF, "Vocк morreu.");
    SetPlayerHealth(playerid, -1);
    return 1;
}