It is not known to evolve into or from any other Pokémon.
Tentaquil is a kind of blue frog/toad of some sort, it has a golden spiral on its belly and long claws, Tentaquil's stomach suffers from such a strong gastritis that it has the power to puke blood with a pressure of 997,999,993 psi holy shit
As of the March 2020 update, Tentaquil is no longer able to trigger the bad ending after defeating the champion.
Design & Name Origin
Do you really not know what Tentaquil is based off of? It's a Tentaquil. Show some respect.
Back in 2010, there was a thread on /vp/ to draw your favorite Pokemon without looking. Someone drew this
When asked what it was, the creator replied "It's a Tentaquil". A romhack was later made called "Pokémon: Tentaquil Edition," in which the player's only Pokémon is Tentaquil with his signature move "Puke Blood". The creator might've meant Tentacool/Tentacruel/Politoed/Quagsire/Cyndaquil.
Tentaquil soon become a hit meme on /vp/, with its signature move of vomiting blood