League of Legends (LoL) Question: How to activate NEEKO's passive? What are the functions?

Clicking on an allied champ? Or their picture?Can I use the health of my ally as a shield or I will still get damage? If I do than how will I know my health? If lux barriers or shields herself, then will I get the barrier at least? Or only her skin, movement speed?
Will it mimic how many stacks of the forth attact TF has and show the cards around her..or him, when she autoattacts reaching that stack? Wasn't this champion more hard to code, than Azir(who had to wait for 1 year to come out, bugfixes creating bugs)? I can't wait, no one can hate this champ, if the real champ casts an ability, she is revealed anyways, Definitely fun and not overpowered, also skill based stun. What else should I know? There is so small information about her. Thanks!