The precursors to Hopping Flames are Super Mario Bros. 3's Fire Snakes. These were chains of fireballs with eyes on the front segment and a trail of smaller fireball segments trailing behind. They aggressively jumped after Mario, but could be destroyed with Raccoon Mario's tail. For Super Mario World, these were reduced to just one fireball segment with no face. They hop toward the player, pause, then hop towards the player again. Every time they land, they leave a small flame burning on the ground behind them. It is possible to spin jump off of the big flame, but the small flame is always harmful to touch.
As would be expected, Hopping Flames cannot be killed by fireballs. A cape swipe will dissipate them, as will a thrown object. Yoshi can eat them, and if they're located on a slope, Mario's slide attack will destroy them.
Hacking informationHopping Flames can only be used with the forest sprite set. (GFX02) By default, they use palette 0A. They are only found in the Special World level Outrageous in the original game, where they littered narrow spaces with unstompable flames and hid behind trees. They are significantly less challenging in open spaces.
Related ROM Addresses
0x09DEC [AE 8E] Hopping Flame's tilemap
0x12417 [AC] Small flame left by Hopping Flame Tilemap
0x0918D  Extended Sprite Hopping Flame leaves behind
0x1244C  Small flame's palette. (Added to Mario's fireball's palette)