Well according to the show he got it for Oseibo already caught and only a year before meeting Ash and company. So I imagine it was right around when Jessie, James and Meowth graduated from being trainees and became an official team. It made sense that Jessie would give it to him since she loooooves him but won’t say. Also he’s her partner and she can’t have him running around with no Pokémon
Koffing are strange airborne chordates with a highly variable appearance. Body cavity is mostly hollow, occupied primarily by a large botryoidal mass of hydrogen-filled gas bladders and a cavernous pharynx densely latticed with mucous webbing for collecting atmospheric particulates. Feed exclusively on pollutants, only existing in the most crowded population centers where the air is foul enough to sustain them. They’d be valuable as natural filtration systems if the gaseous waste they produce constantly in massive quantities wasn’t as/even more toxic than the material they consume.
Cellulose exoskeleton like cartilage in flexibility & strength. Tumorous cellular composition, despite being a naturally brainless meat balloon it’s extremely common for their epidermal layer to grow hair, teeth, even functional mammalian eyes, though they are incapable of interpreting the visual data gathered. The unblinking, glassy gaze and impression of a readable facial expression created by the various surface lumps has led to the common misconception that they’re aware of their piteous existence and suffering. More than a few people have lost limbs or even died in blasts caused by deliberately puncturing koffing and weezing as to ‘put them out of their misery’. In reality it’s unsure whether or not they are even truly sentient. Those who don’t heavily anthropomorphize them usually see them as little more than very dangerous plastic bags.
Rarely a koffing may develop brain tissue within it’s visceral mass. Such individuals, while being more likely to develop into weezing, are no less prone to suddenly and violently exploding at the slightest stress.
Weezing are much more stable than their smaller juvenile form, but also much, much rarer. Weezing may form as the end result of the fusion of several koffing, or of a spontaneous growth spurt in older koffing. As the pokémon ages it’s genetic structure becomes increasingly unstable and more likely to ‘evolve’ into it’s adult form.
Reproduction is spore/pollen based.
The cancerous nature of their tissue, its constant growth and self-mending, means they’re capable of living indefinitely, given they avoid spontaneous combustion. A complete enough fragment of an exploded specimen (whether koff or weez) has the potential to develop into a clone koffing of it’s ‘parent’.
Pigmented dull shades of gray, purple, blue, or, in exceptionally rare instances, green. Eyes can be any color, but are usually brown.