Mmm, try make a portal outside of the gate, so person will use portal to teleport to dragon?
Also you can add some thing like
public int Elvarg = 0;
If you have delta search for
sM("Someone else is already fighting your opponent.");
and add
if(server.npcHandler.npcs[attacknpc].npcType == Elvarg id && Elvarg == 0)
sM("You can't attack Elvarg!");
break;
and to portal add Elvarg = 1;