Basically, mechanics that enable you to punish your attackers with damage and/or crowd controls. Kinda like Thornmail, but not done passively (Maokai and Galio are more what I'm looking at).
Or is "punished for attacking" something that's considered toxic?
Narasimha2 votesAs a passive? No, it goes against a principle of design. The entire point of combat is to do damage and kill the opponent. What you are proposing is a passive that would automatically put the opponent in a position where they would never want to attack you. Thornmail balances itself out because its actually gold inefficient, and all other sources of damage-returning are active abilities.
Fried Noob1 votesYou mean like 
?
Lord OwlBear1 votesI guess I could see it being like a build up passive like 
shield, but instead damages them for a portion of their damage dealt
EndlessSorcerer1 votesDo you mean something like Fiora's Parry, Jax's Counterstrike, or Fizz's Playful Trickster? Or maybe something closer to Annie's Molten Shield or Rammus's Defensive Ball Curl
It might work, but they tend to be pretty binary (either it works great and can counter a particular mechanic or it's very useful). It really depends on how it is handled (cost, downtime, damage or CC duration, etc).
Kingsgrave1 votesI think its better suited for an active so there is a reactive window for the player rather than how Riposte for example works currently. Fiora can throw it out and basically make it like 2 seconds of "you can't hit me or I punish you" rather than "I reacted really well to your attack so i reflect it"
The only thing I can really think of would make the passive way too similar to Pantheon's. Something like "every nth attack or spell you redirect the next attack"
