OK I see that you are fighting PD. Yes he will ignore summons to a certain point, but here are some strategies that I found worked on him. This was on Unfair but without the 2x crit multiplier.
1. SWAMP him with summons. Like, fill his entire local area with skeletons. He MAY ignore them at times but it will help to get his attention.
2. Deny his ability to charge - his charges are what really destroys targets. Use as many Selective Siroccos as you can on his position in order to exhaust him so that he can't charge anymore. Charging is what allows his AI to ignore local targets and pursue backliners, he really doesn't want to lose his full attack iteratives.
3. Try to get him to target a character with the mythic ability that gives them a couple of turns of immortality. They will eventually die but this will buy you a lot of time. Remember that the arcane spell 'Blink' isn't bypassed by any form of True Seeing or similar ability, so its very useful to deny his attacks.
4. Debuff him, this is extremely important. Use the glasses that give you a natural 20 on your dispel roll. You can have two of these per fight if you use the ability on the desired character, THEN rest - the ability will stick, and you have a use of the item left.
5. At the start of the fight, try to use line-of-sight to stop him from charging your squishy characters, I had limited success with this but eventually he charged my tank instead of my backline.
6. Use REACH to discourage him from attacking your main character and any other important damage dealers. By swamping him with skellies, he may frequently choose to attack them instead of your reach character. Lunge is absolutely clutch here, and obviously you can use reach weapons.
7. Use as many AC-lowering debuffs as you can, such as hexes. Works well together with Jinx.
He is very defeatable even on the higher difficulties, you just have to really bring your A-game.
You can of course choose to use swarm strategies on him such as Creeping Doom, this is basically cheating IMO because the swarms are immune to his damage, but whatever, fight cheese with cheese I guess.