How to do labyrinth key runs?

How do you do max key runs efficiently?

According to the wiki, extra keys are dropped by Argus and curious strongboxes. Are these the only way to get keys or are there others? Do the curious strongboxes always spawn behind silver doors or so you have to explore the full lab to get them?

I can't seem to find this information anywhere no matter how much I Google. I want to start doing full key runs in the endgame lab since unlike merciless lab, it drops loot that's actually useful.

You can get treasure keys in the following ways:

1. Killing Argus drops an extra key.

2. Opening a curious locker drops an extra key. (Always behind a silver door).

3. There is a prophecy that makes Izaro drop an extra key.

4. In the first and/or second stage fights, if you allow the mechanic to reach its maximum difficulty, Izaro will drop an extra key. This can be done in each of the phases to stack difficulty and for extra keys.

5. Izaro drops one key by default.

6. One (maybe more, I've seen 2 before) of the treasure chests in the end contains 2 keys.

So assuming you don't do any side areas or content and don't have the prophecy for the extra key, the maximum number of keys you can have going into the treasure room is 3: One each for not doing the mechanic in the first and second stages, and one from defeating Izaro.

If you want more info, just look up Izaro on the PoE wiki. Mechanics of both Izaro and the Labyrinth itself are the same in Merciless and endgame, aside from the new traps and trap layouts (and of course different boss HP/damage).