I've placed Luden's Echo on a number of different champs and with different items. When I place it on someone with very low mana (Yas, Akali, or Lucian with a Seraph's), it only procs maybe every 2 or 3 spells. If they cast slower, it procs every single spell. Is this from a CD on Luden's, or is it a bug, or what?
Pretty sure it has a CD
A lot of mechanics in the game involve a 1 sec internal CD, so maybe 
is no different.
I know of 2 of those mechanics:
Units maintain aggro on their current target for 1 sec, after it goes out their attack range, before they focus a new target. That's why if your 
, on the other side of the board, hooks a champ that your unit are focusing, your units will follow that grabbed target for 1 sec before focusing the nearest enemy available. Or if an Assassin is attacking 
and he dashes away, the assassin will follow lucian for 1 sec before targeting the nearest enemy in attack range, etc.
and 
won't give your unit mana for 1 sec after they cast their spells. That's why sometimes you see units like and 
not gaining mana immediately after casting a spell, even though they're attacking a unit.
Also, keep in mind that will hit only the current target, and no one else, if the the current target of the Luden's holder is more than 1 hex away from his teammates! So the dmg will be done to the current target only and you won't see the splash damage animation of Luden's.
The reason it sometimes doesn't proc on Lucian is because sometimes, his skill doesn't get to the spell part of the damage before his target dies.
If the first part of his auto kills them, Luden's won't proc, but WILL be used up, because he dashed.
It's still OP enough to be relevant, but it is what it is.
That's all very helpful. A couple other questions about :
?
? scale with AP?
