Venusaur in depth
A Rafflesia on top of a toad
The open flower resembles Rafflesia arnoldii, a parasitic plant that lives inside a vine and only exposes its huge, strong-smelling flower. It fits the entire line: the seed planted at birth described in Bulbasaur’s Pokédex is exactly a parasitic relationship told in a friendly tone.
The animal underneath is not a dinosaur. Ken Sugimori has pointed to frogs as a reference, and at this final stage what you see is more like a toad: a broad, rounded snout, separated eyes, warty skin, and the gait of a heavy quadruped. Several toads secrete toxins through their parotid glands, which is where the Poison typing of a plant creature comes from.
The names each go their own way. フシギバナ combines 不思議 (mystery) with 花 (flower), closing the joke that began with the seed and continued with the sprout. In English, Venusaur blends saur with Venus — because of the Venus flytrap, or because of venom — and inherits the dinosaur disguise given to the entire line for the Western market.
What each generation took away from it
In Generation I there was a single Special stat of 100, and when it was split into two from Gold and Silver onward, Venusaur got the best possible outcome: 100 and 100, without losing anything. It had less luck with its types earlier on. In Generation I, Poison was weak to Bug, so Grass and Poison added up to a ×4 weakness against attacks of that type; the type-chart change in Generation II erased that hole.
Generation VI gave it Mega Evolution with Thick Fat, and also made Grass types immune to powder moves, which explains why Sleep Powder, learned at level 15, does not work against any of its relatives. Generation VIII gave it the Gigantamax form: all its Grass-type moves become G-Max Vine Lash, which, in addition to direct damage, wears down opponents that are not Grass-type for four turns. Three registered forms in total, counting the regular one.
Outside battles, it was the cover Pokémon of Pokémon Green in Japan and of LeafGreen in its remake, while Charizard kept the visible share of the lineup.
The order in which it learns things
When it evolves, it receives Petal Blizzard, with 90 physical power, and the list stretches out from there. Leech Seed at 9, Sleep Powder at 15, Seed Bomb at 20, Synthesis at 37, Worry Seed at 44, Power Whip at 51, and Solar Beam at 58. That last detail is worth looking at twice: its strongest special Grass-type attack by level does not arrive until a level at which many playthroughs have already ended. The corresponding TM has existed from the beginning, and that is what you use in practice.
Petal Dance, available from level 1 with 120 power, has the usual problem: it locks the user in for several turns and then confuses it. Leaf Storm and Frenzy Plant hit harder by TM, with costs of their own. For a normal playthrough, the stable combination is Giga Drain with Sludge Bomb, covering what the Solar Beam TM leaves out when there is no sunlight.
As a sun sweeper, it shares the job with Exeggutor, which also has Chlorophyll and comes from the same region. The difference is in the distribution: Exeggutor bets the turn on much higher Special Attack, while Venusaur withstands what the other one cannot, with 80 HP and 100 Special Defense behind it.