Act4

[1] ->Dark Gate->Dark Path->Shadow Path->Onyx Platform->Empty Abyss

Enemies have Curse affix

[2] ->Earth Gate->Earth Path->Crusted Path->Opal Platform->Empty Abyss

Enemies have Ironclad affix

[3] ->Water Gate->Water Path->Slippery Path->Azure Platform->Empty Abyss

Enemies have Obstinate affix

[4] ->Wind Gate->Wind Path->Gusty Path->Basalt Platform->Empty Abyss

Enemies have the Nimble affix

[5] ->Fire Gate->Fire Path->Infernal Path-> Scoria Platform->Empty Abyss

Enemies have the Molten affix

[6] -> Light Gate->Light Path->Blinding Path->Pearl Platform->Empty Abyss

Enemies have Blinding affix

Legion Warrior appears when you enter a platform, considered the boss for each area. No affixes for each Legion Warrior. Once you defeat one, the area becomes an Empty Abyss, allowing general grinding in that area. Once you defeat all Legion Warriors, you automatically go to Act 5, which has only one enemy(beyond Colosseum opponents).

'Path' and 'Empty Abyss' enemies are a combination of the enemies you faced in previous acts (e.g. Murvs, skeletons, flankers, wyverns, etc.). Also note that 'Empty Abyss' enemies keep the same affix in the associated area; for example, fighting an enemy in an Empty Abyss that previously had the Dark prefix still possesses the  affix along with other random affixes.