http://www.runuo.com/community/threads/mob-ignores-tamed-controlled-creatures-attacks-players.533012/

You know how it is ... You spend hours setting up the perfect scenario, getting the dungeon just right, and here comes some tamer with their beetle and mare combo ... in seconds flat, they wreck all of your hard work, swipe the loot, and are off down the trail looking for the next easy score.

 Frustrating, isn't it? Yet, tamers are a legitimate class, and one cannot simply increase the monster value in order to give the tamer a challenge, else the hardworking mages, archers, and warriors will miss out on the fun ... what to do, oh what to do? If only there was a way to create a monster that would happily aggro on players without jumping on every fully trained and leveled uberpet that wanders into their domain.

 Well, it seems there IS a way: simply drop this little piece of code into your monster's script, make sure it has fightmode.Aggressor set, and your creation will happily ignore that WW, but jump on the tamer like ugly on an ape as soon as the tamer gets close enough:

 //Mob aggro on player instead of pets by Seraph035//
 public override void OnMovement( Mobile m, Point3D oldLocation )
 {
 if ( m.InRange( this, 10 ) && m is PlayerMobile)
 {
 if ( this.Combatant == null )
 {
 this.Combatant = m;
 }
 }
 }
 //Share and enjoy//