There are many mysterious and strange species lurking in the Pokémon world. Whether it is genetically curious Pokémon like Ditto, who can transform into any other Pokémon it likes, or the terrifying Mimikyu who impersonates a Pikachu to hide its true form, many Pokémon species are shrouded in mystery. One of these strange Pokémon is Tangela. Wrapped in a tangle of blue, noodle-like vines, Tangela's true form has remained a mystery to many fans over the past generations of the series.
Tangela is a Grass-type introduced to the Pokémon series in generation 1. While it didn't originally have an evolutionary form in the first 3 regions of the Pokémon series, Generation 4 introduced Tangrowth. This evolution is a bigger and weirder version of Tangela including arms with long, vine-like fingers while still having some of Tangela's defining features like its large, round eyes and red feet.
At no point in the Pokémon games or animated series has Tangela been seen without its vines. In fact, even its Pokédex entries don't include any information on what could potentially be hidden under the blue mass. According to Pokédex entries spanning every Pokémon game Tangela appears in, its true form remains unknown. To make this Pokémon more unsettling, Tangela wiggles its vines constantly to unnerve its opponents in battle. It is also stated the vines can be snapped off easily, and don't appear to cause any pain to the Pokémon hidden underneath.
Tangela Could Be A Water Pokémon Like Shellder
There has been a good deal of speculation from fans on Serebii about what could possibly be living under Tangela's vines. A popular theory is that it could be the Water-type Pokémon Shellder. Shellder already has a history of combining itself with other Pokémon, like when it bites a Slowpoke to become Slowbro or Slowking. There is also a theory that there is a small, humanoid-like being trapped in the vines, or even just a pair of large, blinking eyes.
Another theory is that Tangela is the Ghost-type Pokémon like Ghastly, who is using the vines to hide when walking around. Ghastly and Tangela both have large eyes with tiny, black pupils, and the similarity makes this theory more compelling. Like many other mysteries in the Pokémon series, Tangela's true form will likely remain a point of speculation for those who pick up the games and nothing official has ever been shared about what's really underneath those vines.
Source: Serebii