From my Perspective on my Master Mode Summon Only. (atm last mech, so Plantera and onward will be a "what it might be like")
King Slime 3/10 . Had Rocket Boots and Horseshoe when I fought, platforms ftw.
Eye of Cthulhu 5/10 . Smacked me a few times, but eventually got him, barely.
Eater of...