Run around while hitting him with spells back, try to do it in circle motion to not get caught up with his spells.
Be carefull to not stay too close when he is casting skill, you can take Jack Wave on, but Jack Impact kill even good geared heros.
If you are really weak, you can drag Jack to right upper part of city where soldiers train, when he engage in fight with Ivan, just finish him off from range. Ivan is very tanky so he can hold long.