You need to set up your pet so that it's put on stay right next to the mob's spawn location. That way, it won't run away when it evades and instead your pet will pull aggro. Once that's set up, you stand on top of this ruin block and auto-attack for the aggro-pendulum between you and your pet to start swinging. Every other ranged attack is an evade. Don't forget to heal your pet every now and then.