[intoxicadooo]

creo que asi es mas facil

PHP Code:

#include <amxmodx>
#include <hamsandwich>
#include <zombieplague>

#define PLUGIN "[ZP]Damage x 2"
#define VERSION "1.0"
#define AUTHOR "intoxicadooo"

new g_item, g_dmgx2[33], g_maxplayers

public plugin_init()
{
       register_plugin(PLUGIN, VERSION, AUTHOR)
    
       g_item = zp_register_extra_item("Danio x 2", 20, ZP_TEAM_HUMAN)
    
    g_maxplayers = get_maxplayers()

    //Eventos
       register_event("HLTV", "event_round_start", "a", "1=0", "2=0")
        RegisterHam(Ham_TakeDamage, "player", "fw_TakeDamage")

}

public zp_extra_item_selected(id, itemid)
{
       if(itemid == g_item)
               g_dmgx2[id] = true
}

public fw_TakeDamage(victim, inflictor, attacker, Float:damage, damage_type)
{
        if (victim == attacker || !(1 <= attacker <= 32))
            return HAM_IGNORED;
        
        if (g_dmgx2[attacker])
             SetHamParamFloat(4, damage *= 2.0)

    return HAM_IGNORED
}

public event_round_start()
{
        for(new id = 1;id <= g_maxplayers;id++)
    {
            if(g_dmgx2[id])
                    g_dmgx2[id] = false
        }
}
public client_disconect(id)
    g_dmgx2[id] = false