Idea for Achievement.

[Zxeres]

Starting in 867 gain all dynasty legacies before 1066. Nough Said.

 

[Zxeres]

It's actually a hard achievement, instead of these vague achievements, where you just have to do exactly what they are asking for under pretenses to get you to the point where you understand the game.

 

[Zxeres]

And while I'm on here talking to myself, witchery is SO super powerful, I hope you guys know that.

 

[Nawjak]

Starting in 867 gain all dynasty legacies before 1066. Nough Said.

For only the base game dynasty perks, you need more than 250 Renown per month for the entire duration (which means significantly more in later years as you start out small).
If you want to use artifacts by using the Royal Court DLC, you have five perks more, so you need more than 330 Renown per month.
Would you also count legacies added by Northern Lords or Fate of Iberia? You can get them all by being North Germanic and have your capital in Iberia, for only 750 Renown per Month if you want to unlock them before 1066.

I dare say it's impossible if you don't happen to actively use the renown bug of the "Secure the Mediterranean" decision where the renown bonus was applied for all dynasty members... (or use other cheesy shenanigans).

And while I'm on here talking to myself, witchery is SO super powerful, I hope you guys know that.

If your witch coven has a couple hundred members, holding a grand rite stops the game for a few seconds (I have to add that this is an observation from a modded game, don't know if you can get to that point in an unmodded game)