If you played magic in the early days you would have been fearful of the mighty Shivan Dragon. A flying 5/5 Dragon with firebreathing, that was capable of threatening you life total in a hurry. While it has been surpassed by newer cards, the firebreathing mechanic is still being printed especially on Dragons. Dragonrage is the only instant way to grant the ability, which additionally acts a ritual. Making it a fine addition to Card of the Week.
Dragonrage is an instant for 2R, that adds a red mana to your mana pool for each attacking creature you control. Additionally it gives each attacking creature you control firebreathing until the end of turn. Firebreathing is an activated ability that costs a red mana and gives the creature +1/+0 until the end of turn.
This is best in a deck that is running a lot of creatures and looking to attack anyway. For example if you are running a Goblin token deck you can generate a lot of mana and use it to cast combat tricks. If you don’t have any you can always pump the mana into the firebreathing ability of an unblocked creature. Additionally if you are looking to play more of a spellslinger build, you can generate the mana and cast more spells.
However, as a ritual it is quite unreliable. This is because you need to be attacking with at least 4 creatures for it to be positive. Furthermore as you can only create the mana from attacking creatures, you can only create it in your combat phase.
Dragonrage is best in a deck that seeks to flood the board with creatures and turn them sidewards. You can generate a large amount of mana, which can be turned into damage. Commanders include: Krenko & Krenko; Kykar, Wind’s Fury; Brudiclad, Telchor Engineer or the Locust God. If you are playing an infect build of Saskia the Unyielding it could be useful as a pump spell. In Kalamax, the Stormsire you can copy it when you cast it to generate even more mana.
My personal favourite is Adeliz, the Cinder Wind. Ideally a wizard tribal deck that is looking to take advantage of the pseudo prowess she grants. Dragonrage would likely be mana positive and allow you cast even more spells. All of these decks would also appreciate a previous Card of the Week First Day of Class.