From the Super Mario Wiki
“Step right up, if you're ready to get toasted!”
Tryclyde, also known as Triclyde, is a large, three-headed snake capable of breathing balls of fire. He is also an inhabitant of Subcon, the land of dreams. His design is based on the mythical Lernaean Hydra, a giant, multi-headed serpent.
Not much of Tryclyde's past is revealed, though it is mentioned that he was originally a loner and outcast who was shunned by others due to his cunning mind and evil tendencies; due to these traits, Tryclyde was recruited by Wart in his plot to take over Subcon.
 Super Mario series
 Super Mario Bros. 2
In Super Mario Bros. 2, Tryclyde acts as the guardian of World 2 and World 6 and upon sighting the player, will shoot fireballs at them. In order to injure Tryclyde, the player would need to throw several Mushroom Blocks at him, which were resistant to Tryclyde's fire breath. After being hit by 3 Mushroom Blocks, Tryclyde would be defeated.
While Tryclyde reprises his role in the version of Super Mario Bros. 2 included in Super Mario All-Stars, he is only the boss of World 2 in the Super Mario Advance port, having been replaced by a Mouser in World 6.
 BS Super Mario USA
Tryclye returns with the other bosses from Super Mario Bros. 2 in BS Super Mario USA. Like in the first game, Tryclyde serves as a mini-boss, and is fought in a similar way as in his battle from Super Mario Bros. 2.
Tryclyde appears to have a green coloration in this game (though he has been updated to being a blue color in the other remakes of Super Mario Bros. 2).
 The Super Mario Bros. Super Show!
Tryclyde (voiced by Harvey Atkin) is featured in several episodes of The Super Mario Bros. Super Show!, which depict him as being quite powerful, though somewhat unintelligent. Instead of working for Wart, as he does in Super Mario Bros. 2, Tryclyde works for King Koopa as a member of his Koopa Pack, often appearing to help him, Mouser and Koopa Troopa in their plots. Also, despite being shown to talk in The Super Mario Bros. Super Show!, Tryclyde rarely did so. He most often battled Princess Toadstool, who was usually able to defeat him.
 Nintendo Comics System
Though Tryclyde never made a direct appearance in any issues of Nintendo Comics System, one of the comics' Dear Princess Toadstool features had him writing to Princess Toadstool in a thinly veiled attempt to get a date with her. In the letter, Tryclyde refers to himself using words such as "we" and "we're", which implies that he actually has three independent minds in his three heads, instead of one central mind.
 Nintendo Adventure Books
In one of the bad endings of Pipe Down!, Ludwig von Koopa plays a mournful tune on a harmonica to summon Tryclyde to attack Mario and Luigi. Before the heroes can react, Tryclyde grabs them both by their rears, and drags them off to his lair.