Missing Logs? (Anniversary Update)

[Birdi]

Missing just a few things in the Logbook, no idea what some are.
I'm missing the Captain's Legendary item somehow.. it can't drop so how would I unlock it?

A monster between Elder Lemurian and Lunar Chimera that's shown as Locked? Mithrix's log?

And the two Environment Logs I'm missing now are the final level's, and some unknown hidden realm below Void Fields'.

Any help?

[Rose]

Captain's Legendary you can get by killing a Captain Doppelganger or trying those Altars that turns all your items (by tier) in one item of each tier that you have on your loadout.

Yas, it's Mithrix log.

Final Level you have 5 minutes to find it. And this one under Void Fields, I do want to know about this one too, and I have no clue.

[Skintanium]

Seconding the Captain's doppleganger. use the artifact of Vengeance and do not pick up any items before the doppleganger spawns. The missing environment log is allegedly the test stage and should not be in the logs as there's no actual entry for it.