When you die, you now control a poro that spawns at your corpse.
It can be killed, but it will respawn again immediately to the closest area which is revealed by ally vision.
A poro can move around but grants no vision. It must stay inside ally vision. If a poro moves into the darkness, the darkness will kill the poro instantly (poros are terrified of the dark)
A poro will not absorb a collide on hit skillshot (ezreals mystic shot) but it will pass through the poro and kill it.
A poro takes least priority if it were to be targeted by a targeted spell (you can't pile up on your ally to cause the enemy to miss a baleful strike)
A poro is just a goof around sort of mode that you can fool with while waiting to respawn. The number one rule of implementing poros is: #####it doesn't actually interact with your chances of winning or losing.
Poro's only have a few abilities. They can burrow beneath the ground to reappear wherever they want (in ally vision). Maybe they can have a few others that only interact with other poros.
Being able to be killed by an enemy champion makes you feel vulnerable, and not being able to fight back kind of makes it fun. How close can you skirt outside the enemy's vision without being caught and killed? Its just as much fun as you are willing to make it.
A poro spawns invisible to enemy champions but can make itself visible by using a poro ability. It can only use the abiliity when within 1400 units of an allied champion (that is the range of natural sight), and it tethers to the allied champion with a tether that only the poro can see. The tether will break on contact with terrain. As long as the tether persists the poro will be visible to enemy champions.
This is just to make it so that you can't reveal the general location of a ward by revealing yourself as a poro to an enemy champion in the location where a ward gives you ally vision-- remember, the number one rule of poro implementation is that it doesn't interact with your chances of winning or losing.