Köszönöm nektek a tippet, tanácsot!

#include <amxmodx>
#include <amxmisc>
#include <engine>
#include <fun>

#define PLUGIN "New Plug-In"
#define VERSION "1.0"
#define AUTHOR "author"

new g_MaxPlayers

new cvar_invisible_factor

public plugin_init() {
   register_plugin(PLUGIN, VERSION, AUTHOR)
   
   register_think("check_speed", "Set_Furiens_Visibility")
   
   cvar_invisible_factor = register_cvar("fr_invisible_factor", "1")
   
   g_MaxPlayers = get_maxplayers()
}

public Set_Furiens_Visibility(iEnt)
{
   entity_set_float(iEnt, EV_FL_nextthink, get_gametime() + 0.1)

   new Float:fVecVelocity[3], iSpeed

   for(new id = 1; id <= g_MaxPlayers; id++)
   {
      if(!is_user_connected(id) || !fr_core_is_furien(id) || !is_user_alive(id))
         continue;

      if(get_user_weapon(id) == CSW_KNIFE)
      {
         entity_get_vector(id, EV_VEC_velocity, fVecVelocity)
         iSpeed = floatround(vector_length(fVecVelocity))
         if(iSpeed < get_pcvar_num(cvar_invisible_factor)*255)
         {
            set_user_rendering(id, kRenderFxNone, 0, 0, 0, kRenderTransAlpha, iSpeed/get_pcvar_num(cvar_invisible_factor))
         }
         else
         {
            set_user_rendering(id, kRenderFxNone, 0, 0, 0, kRenderNormal, 0)
         }
      }
      else
      {
         set_user_rendering(id, kRenderFxNone, 0, 0, 0, kRenderNormal, 0)
      }
   }
}