Ludden's Echo or Rabadon first on Lux?

Echo for mobility and you don't have as much AP to boost with deathcap. Zhonya, RoA, and some situational items are also good first depending on game scenarios.

You really need to think about and as potential buys and nearly it always depends on your team/the enemy as to which of the four you want next.

Luden because first item Rabadon is useless.

I always always always go Morello, rabbies, Rylais (for the slow and sustain) then go ludens echo and finish it off with abyssal and of course magic pen boots somewhere in there

So after Morellomonicon... do you recommend going Ludden's next or Rabadon next? Why?

is better earlier in the game rather than later due to the passive.

is better later in the game rather than earlier due to the passive.

Really depends when you need to put your carry pants on. If you're time to shine is mid-game, Echo is the way to go. If it's late game, the party-hat is the better buy.

My personal preference is usually Echo, but if the enemy team is packing a lot of MR and antimage capabilities you're not gonna do much mid game.

I'd usually recommend thinking about it as 1 or the other though. is pretty much always the best 3rd major item (no magic pen usually insures you're a glorified support against any juggernaut or tank), and an average game usually only lasts long enough to complete 3 major ~3k items.