Forgotten Tales

How many keys (1 and 2) can I have in inventory at the same time? I've seen posts that say only 1 at a time (of either kind), yet there are YouTube posts which show completing the quest without killing a single mage (guessing they acquired multiple keys beforehand).

In General Information, there's the item lists...
I don't recommend the pdf - I think it's out of date still, but I'm not sure; I honestly prefer text files as pdfs are so slow.
So I never check the pdf

Most of the time, I will recommend items.txt
But there is different info shown in items.list, which is where I got this

340 337 QUEST Blue Key 1 UNIQUE:1 NON_TRADABLE:1
341 338 QUEST Blue Key 2 UNIQUE:1 NON_TRADABLE:1

UNIQUE - this means, if you have one, you will not get another drop; it can be on your screen and you won't get one either
NON_TRADABLE - you can't give it to others, or put it in storage

I don't watch the youtube videos.. but it's quite possible it was edited.
For the blue maze, you need to stop and kill at points to get a new key - as you can only carry one at a time.

The youtube videos were taken when the blue keys were tradeable and had no restrictions.

Right, when those quests were introduced, the "non-tradable" mechanic was not working properly. Players would go get a key, and put it into a clan storage building, then go get another etc... Then lower level players could just grab the keys they needed from storage to go do the quests without having to kill anything to get them. It was exploiting a game mechanic (or even abusing a bug) both of which are obviously bad... but to be fair it was also pretty fun to see the clans working together to help each other lol :p

At any rate, it has been fixed now, so you'll need to do a fair bit of killing during the quest because you can only hold 1 at a time of each key

Thanks for clarifying!