Throughout the series, most of the dragon transformations available to Ryu can be divided into three "tiers," each of which contains a group of dragon-forms that share a basic sprite (with the color-palette swapped to distinguish different forms), similar abilities and attack strength, and a comparable cost in AP for each use. The forms available in any given tier tend to be larger, more powerful, and more expensive than the previous group. There is also his "ultimate power," the nature, appearance, and usage of which tends to vary extremely widely from one game to the next.
The first and weakest type of dragon transformation, created by the earliest-available or the simplest type of dragon transformation, and capable of attacking only a single enemy with its breath weapon. In the original Breath of Fire, there are three analogous forms known as "Drakes" – the Flame Drake (FlmDr), Snow Drake (SnoDr), and Thunder Drake (ThrDr), each of which deals fire, ice, or lightning damage with its breath attack, respectively – all of which are obtained after Ryu defeats the trial in the first Dragon Temple, just after the Stone Robot scenario. In BoF2, the corresponding "Puppies" – Fire Puppy, Ice Puppy, and Thunder Puppy – are obtained in a scripted event after clearing out the well-dwelling monsters in Capitan. In BoF3, the basic dragon forms are called Whelps for the first time, and are produced by using any single Dragon Gene other than Force, Fusion, Infinity, or Miracle; they have slightly more HP than Ryu in his natural state, and about twice his physical attack power.
The second type of dragon transformation, created by a more advanced or complex type of dragon transformation, and capable of attacking all enemies with its breath weapon. In the original Breath of Fire, there are four Dragons – Bolt Dragon (BltDgn), Fire Dragon (FirDgn), Gold Dragon (GldDgn), and Ice Dragon (IceDgn), each of which deals lightning, fire, holy, or ice damage with its breath attack, respectively – all of which are obtained after Ryu defeats the trial in the second Dragon Temple, located down the path between the Dark Dragon pyramid and Nabal Castle. In BoF2, there are three Dragon forms – FireDrgn, IceDrgn, and T.Drgn which are obtained after Ryu speaks to the Dragon Elder hidden behind the waterfall next to the Wildcat Cafe; however, due to a glitch in the game, these forms deal only non-elemental damage. In BoF3, Dragons are the most frequent result of combining two or more Dragon Genes, although different combinations produce Dragons with very different traits and abilities, and certain combinations produce entirely different dragon forms (most of which are noted below); the abilities of Dragons are generally higher than those of Whelps.
The third, most powerful, and often inexplicably renamed-in-translation type of dragon transformation, which consists of a single dragon capable of attacking all enemies with its breath weapon for massive non-elemental damage. In the original Breath of Fire, "Rudra" is obtained after Ryu defeats the trial in the third Dragon Temple, located on an island northwest of Gust. In BoF2, the "G.Drgn" is obtained in a scripted event within the Grand Church. In BoF3, the properly-named Kaiser is created by any combination of Dragon Genes that includes the Infinity Gene, but acts completely out of the player's control unless it is combined with either the Failure Gene (producing a weaker but controllable Kaiser) or the Radiance and Trance Genes (producing a more powerful and controllable Kaiser); in this version, Ryu's form does not change much, but his abilities increase, and he is able to summon a giant dragon that strongly resembles the Kaiser from BoF2 when he uses a breath attack. In BoF4, the Kaiser is actually the second dragon transformation Ryu obtains, after (initially) losing the battle at the end of the second chapter; as in the previous game, the Kaiser remains berserk and uncontrollable until you have acquired all of the other Dragon Summons.
The hero's ultimate power, which was renamed-in-translation almost as frequently as the Kaiser. In the original Breath of Fire, "Agni" combines all of the members of the party into a single, immense hybrid dragon with tremendous attack and defense power; it is obtained in the cave near Romero, from a hidden Dragon Shrine located underneath the pool of Cleansing Water, and is required to get the game's good ending. In BoF2, "Anfini" is a one-shot power that Ryu cannot use until he faces Deathevan's true form, at which point it revives all of his party members for the final battle; it is obtained in the Dragon Temple located just below Dragnier. In BoF3, Infinity is simply the name of the Dragon Gene that unlocks the Kaiser transformation. In BoF4, Infinity is a dragon transformation that only appears during a scripted event.
A type of dragon transformation first appearing in BoF4. It is Ryu's initial transformation, and is obtained quite early in the game compared to the dragon transformations of the previous games. The Aura Dragon is obtained as a scripted event, right after Fou-Lu obtains the Astral Dragon Transformation. Its traits are roughly equivalent to those of a Whelp in BoF3, and it has an assortment of flame-based and defensive magic, as well as a non-elemental breath weapon.
A type of dragon transformation first appearing in BoF4. It is Fou-Lu's initial transformation and the equivalent of Ryu's Aura Dragon. The Astral Dragon is obtained as a scripted event near the beginning of the game, and is the first dragon transformation to appear. It has an assortment of water-based and death magic, as well as a non-elemental breath weapon.
An extremely large dragon transformation first appearing in BoF3, which replaces all members of the party on screen when created. Behemoths are created by combinations that use the Miracle Gene (but not the Failure, Force + Trance, Fusion, Infinity, Reverse + Thorn, Shadow + Trance, or ??? Genes), and tend to have high HP and defense, but very poor speed. There is a "Golden Behemoth" known as Mammoth, which is created by combining the Miracle and ??? Genes; it has even higher HP than any other dragon form, but has very low defence. In BoF4, Behemoth is obtained by acquiring the Earth Gem from the large, tree-covered island between Pabpab and Saldine; it retains the traits established in the previous game, and gains various earth-based abilities. It later upgrades to Mammoth.
A special class of dragon transformations appearing in BoF3, which create unique dragons whose appearance reflects one of the other party members. Hybrids are created by combinations that use the Fusion Gene, and their stats and abilities vary widely depending on the character Ryu has fused with.
A unique and tiny dragon transformation first appearing in BoFIII. The Pygmy is created by combining the Mutant and ??? Genes; other genes have no effect, except for Failure, Fusion, Infinity, and Miracle (which unlock their respective special forms). The Pygmy's attack, defense, and HP are all very low, but it is extremely fast and agile, as well as having an extremely potent breath attack. In BoFIV, a Pygmy-lookalike named "Mutant" is obtained by acquiring the Flawed Gem from the En Jhou Ruins; it retains the traits established in the previous game, and gains status-affecting attacks. It later upgrades into Punk.
A dragon transformation first appearing in BoF4. It is Fou-Lu's equivalent of the Wyvern, and is obtained by acquiring the Water Gem from the Sanctuary. It has water-based spells and attacks, and it later upgrades to Peist.
A unique and large "Dark Dragon" dragon transformation appearing in BoF3, which replaces all members of the party on screen when created. Tiamat is created by combining the Shadow and Trance Genes; other genes have no effect, except for Failure, Fusion, and Infinity (which unlock their respective special forms). Tiamat has high stats overall, low AP cost and is extremely resistant – possibly immune – to status effects.
A "Golden Dragon" form appearing in BoF3. Created by combining the Flame, Frost, and Thunder Genes, Trygon has average stats, immunity to fire, ice, and lightning damage, and the ability to use four different elemental breath weapons (fire, ice, lightning, and non-elemental). However it lacks in terms of single-target damage.
This is Fou-Lu's Kaiser-equivalent dragon transformation in BoF4. It is obtained automatically after Ryu obtains the Kaiser.
A type of dragon transformation first appearing in BoF3, which gives Ryu a dragon's wings and claws while leaving the rest of his body more or less unchanged. Warriors are created by combinations that use the Force Gene (but not the Failure, Fusion, Infinity, Miracle, or Trance Genes), and tend to have about the same HP as a Whelp and average defense, with amazing attack power and speed. There is a "Golden Warrior" known as Myrmidon, which is created by combining the Force and Trance Genes; all of its stats are increased over the Warrior's, and it gains a different assortment of special attacks. In BoF4, all of the dragon transformations initially turn Ryu into a form resembling the previous game's Warrior, with the true dragons appearing in "summoning sequences" whenever he uses a breath attack. BoF4 also features the Myrmidon, which is obtained by acquiring the Wind Gem from the area west of the Emperor's Tomb, where the forest burned in the opening chapter; it retains the traits and abilities established in the previous game (albeit more wind-based) and later upgrades into Knight.
A "Golden Whelp" form appearing in BoF3. Created by combining the Miracle, Reverse, and Thorn Genes, Wildfire has extremely low HP, as low as 17, but its other stats (especially Attack and Defence) are above average. If it manages to survive a turn, it will do over 600 damage on a single shot.
A type of dragon transformation first appearing in BoF4. It is obtained by acquiring the Flame Gem from the Mount Giga area, and has flame-based spells and attacks. It later upgrades into Weyr.