Here are some of the champs from a guy who's already completed LOL once... he obviously went straight from the start point and didn't make the right turn but I'm not sure what paths look like beyond Red Hulk for him to fight these specific champs:

RedHulk (hard fight had to evade his sp's or Sw would almost die with a block..)

Old Man Logan (was always on regen long fight plus sp 1 & 2 was unblockable make sure too remember that or you can bleed out)

Elektra (hard fight if u got hit u would almost bleed to death & I found evading her sp1 very tricky)

Mrs Marvel (easy fight had plenty of practice with cap marvel in the original rol)

UC (hard fight just have to remember not to attack when his done a sp..evade until unstoppable wears off)

Golden Adaptoid - (reward x1 5* sig)

The Vision (easy fight just watch out for the sp1 got me a few times)

Spider Gwen (she was hard activating her sp 1 was giving her crazy evade try to wait for it to wear of or keep hitting so she does sp 2 instead)

Cyc (as long as your gd at evading his sp 1 & 2 your gd)

Falcon (very tricky to fight him sometimes he would save for 3rd sp)

Gamora (one of the easiest fights sp so easy to evade)

Magik (every time she was doing any sp I was also losing a lot of health but easy to fight)

War Machine (his armour was crazy but easy to evade his sp)

Antman (was a nightmare nothing was working with Sw & hitting him were so low it took ages this was the longest fight apart from maestro)

DPX (alway on regen just keep hitting him & watch out for the boost he gets too 3rd)

Daredevil (1st & 2nd sp does not hit him leaving u open for attack.save for 3rd)

Venom (really fast just like he was as a boss in the last aq)

Iron Fist (hits hard try not too get hit)

Civil Warrior (does his 1st sp a lot so be ready for it)

Maestro (evade every special attack or u die