can proc on quite literally any "technically active" spell effect.
's plants proc it.
's turrets proc it.
's shrooms proc it.
's traps proc it.
's boxes proc it.
's ghosts proc it. (Right?.. I've just... never seen him...)
Is this healthy? Spells left to their own devices dealing 100 (+15% AP) more AoE damage than they're meant to? Damage that can be potentially global?
Edit: Calm down with those downvotes, people, this basically a survey.
Keitron1 voteswhat i hate is that gp Q does no proc
ABlueQuaker2 votesBecause GP's Q is treated as a Melee Auto-Attack.
Hupsis1 votesIt procs 
FantasySniper1 votesFizz can proc with his, though...
lolipopevelynn1 votesit works like rylais. what are u even talking about
ABlueQuaker1 votesIt's fine because they still have to be Casting or Moving for Luden's Echo to build up charges.
DrNova1 votesLE doesnt do a ton of damage on the proc. Good for waveclear, but come on it isnt going to do anything but tickle most anyone elsel
FantasySniper1 votesWith enough given procs, that damage stacks. Teemo or Nidalee can be dicking around and still be getting an Echo proc on every trap they step on.
Marthian1 votesThe big issue I see all the time is when the other person doesn't do anything to proc it. It really should proc on active spell effects, not "passive" (like the ones mentioned) It shouldn't proc on DoT effects mid-DoT either (such as when it procs on the third damage tick) only on the first damage tick.