The Fire Flower has never fully appeared yet, but in The Great Prophecy, it appeares as a regular fire flower that's black and white.
The Rise of Gonzo
The Fire Flower's first and only appearance so far is The Rise of Gonzo . When Toadsworth showed Mario the Great Prophecy, it explains how the world got destroyed 100 years in the future. In the Great Prophecy, Gonzo found the Fire Flower and went crazy and destroyed everything. However, Mickey and Toadsworth came up with a plan where Mario goes into the past, gets the Fire Flower, and destroyed Gonzo. Mario accepted this plan and was about to go when Toadsworth gave Mario the special map that leads to the Fire Flower. Mickey gave Mario his only time string to travel into the past, but Mickey and Toadsworth were all out of time stones. So Mario had to travel into the past without Mickey, possibly never seeing them again.
When Mario got to the past, he told Luigi, Jack, Yoshi, Peach, and Sylvester about what happened in the forest and in the future. A little bit later, Gonzo was at the door and knocked and rang the doorbell. Everybody ran and Mario and Luigi decided to escape and start their journey to find the Fire Flower from the backyard. Gonzo busted inside the house with his lightning and spotted Jack, who was hiding, but his legs were in the open, shaking. Gonzo told Jack to tell Gonzo where Luigi was. At first, Jack wouldn't tell him anything and slapped him, but Gonzo threateneed to turn him into ash. So, Jack told him that Luigi left with Mario and they're going on a journey to find the Legendary Fire Flower, to put a stop to Gonzo once and for all. Gonzo asked Jack where the Fire Flower was, but Jack didn't know, so Gonzo just shoved him aside.
Meanwhile, Mario and Luigi were climbing a little hill. Mario got out the special map that lead to the Fire Flower, looked at it, and started their adventure.
After collecting all the pieces of the key to the temple to where it was located, they went to get the Fire Flower, until Gonzo destroyed the building. Mario used the Fire Flower to fight Gonzo, until Kermit knocked it out of him and gave it to Gonzo, which made Gonzo transform into Perfect Gonzo. He easily beat Mario and Luigi, until Kermit attacked him and gave it to Luigi. Gonzo had become furious and had somehow matched the power of Fire Flower Luigi, he tried to vaporize him until Mario helped Luigi destroy Gonzo once and for all.