Back when Tigers used to smoke.
I've always found the Porygon line to be an interesting one, specifically it's capabilities outside of traveling in virtual space. I think we all know that Porygon can travel in virtual space but as demonstrated in Pokemon Adventures, something like Ash's Muk attempting to suffocate Porygon would just not work. Porygon is a resilient if not almost nigh-indestructible Pokemon that is capable of surviving in any extreme environment that would be lethal to most Pokemon & humans including outer space. It's a man-made Pokemon that does not need to breathe oxygen and does not need to eat to survive.
Porygon2 is a scarily interesting one because not only does it gains the resilience of Porygon before it but it's intelligence is enhanced to the point that it's able to do things outside of it's programming including learning new behaviors that you have to wonder, is this artificial intelligence like the Pokedex claims or is this real intelligence.
Finally there's Porygon-Z which I find especially interesting around the time of Gen 7. Porygon-Z was designed to have the function of traveling through alien wormholes as in this Pokemon was supposed to have a power similar to that of Solgaleo, Lunala, Necrozma and in a way this makes sense as Porygon's next evolution. Porygon was a Pokemon designed to survive in extreme environments including Outer Space and it's able to travel through virtual space so the next natural step after Porygon2 is alien environments that are beyond human understanding. Unfortunately Porygon-Z's dubious disc contained a dubious error, who would've seen that coming lol? It's implied in the Pokedex that this power never came into fruition but it's nevertheless pretty interesting because it's possible that whoever was working on the dubious disc was also perhaps researching on Ultra Wormholes. It would've been cool if Gen 7 explored this little detail about Porygon-Z.
There is one animal that the Porygon-line does remind me of and that is the Tardigrade which like Porygon is also an indestructible organism that is able to survive extreme environments including outer space but the obvious difference between the two is that's a micro-animal that suspends it's metabolism, Porygon is a man-made Pokemon designed to be indestructible.