Elder mage boss needs rework. With a poison build it's trivially easy, and with most other builds it's not hard, just time-consuming. My takeaway is to never play enchanted swamp on endless unless using poison build.
The attacks of his allies are easy to deal with if you have at least 4 energy per turn (you need more in endless mode). Given the nature of the elder mage, armor and dodge are actually completely useless during boss fight. Robot toy seems like a great way to kill allies, so I guess that about covers the entire fight. Does robot toy trigger dodge?