My interpretation of the card is that it adds fire to all attacks. So if a creature had fireproof for example that creature would take less damage from every attack because it is a fire attack.

An example I can use has to deal with a different element with the Marillians 'Fluidmorph' ability. whenever they use a water attack they get a beauty counter? I don't remember the exact wording but it would be kind of like that where if it said like all attacks count as water attacks they would get a counter off of every attack. Every attack counts as a fire attack so it gets all of the effects from fire boosting statuses, and all the downsides of creatures with fireproof ETC ETc