The Signer Dragons are a series of DragonSynchro Monsters introduced in Yu-Gi-Oh! 5D's. These legendary dragons play a part in the legend of the Crimson Dragon, as well as them being connected to the Signers themselves. That connection being that these legendary beasts, who actually joined forces with the Crimson Dragon, were the ones who sealed an evil within the Nazca Lines.
The Limit Over Accel Synchro monster is considered to be the ultimate type of Synchro Monster. In the anime, summoning a Limit Over Accel Synchro requires the duelist to achieve Over Top Clear Mind. Reaching this state will cause the duelist, and their Duel Runner to become a shining gold color, implicating the god-like power involved with performing this type of Synchro Summon.
Limit Over Accel Synchros are Synchro Summoned in a similar way to Cosmic Synchro Monsters. However, they do not require their corresponding Signer counterpart in their summoning requirements. They use 2 normal Synchro Monsters, plus 1 Tuner Synchro Monster, which is the same to how Delta Accel Synchro Monsters are Synchro Summoned.
"Shooting Quasar Dragon" must be Synchro Summoned, and it cannot be Special Summoned any other ways. However, despite this downfall, it is able to attack once for every Synchro Material Monster used to Synchro Summon it, and it can negate one card or effect per turn. It can also call for backup by Special Summoning a "Shooting Star Dragon" from the Extra Deck if it ever gets removed from the field. In the anime, it was Synchro Summoned using all of the other Signer Dragons (the exception being, of course, "Stardust Dragon") as Synchro Material Monsters, utilizing the effect of "Life Stream Dragon" to reduce their Levels to 1.
"Life Stream Dragon" is the only Signer Dragon to have a downgraded form, "Power Tool Dragon", which is a mechanized/shell form of itself. "Power Tool Dragon" searches for Equip Spell Cards and cannot be destroyed when it is equipped with one. This sets up for "Life Stream Dragon" who uses Equip Spells in the Graveyard for protection.
Despite the fact that "Stardust Dragon", "Ancient Fairy Dragon", "Red Dragon Archfiend", "Black Rose Dragon" and "Life Stream Dragon" fought against the Earthbound Immortals in the past, the Crimson Dragon did not awaken the true form of "Power Tool Dragon" in the present when it was going against Devack (a Dark Signer with the very Earthbound Immortal it had defeated 5000 years ago).
It appears that creating new copies of the Signer Dragons cannot be done without imperfections - when Paradox stole Yusei's "Stardust Dragon" by absorbing its spirit into a blank card, the resulting copy was a black-bordered card with a mirrored image, something that was not observed in any of the other cards that Paradox copied. The hologram of the monster, however, was unaltered. In contrast, the card copies of "Red Dragon Archfiend" that Lester created were identical to the real card, but the holograms of the monster itself replaced the red coloration with yellow, purple, and teal, a different one for each copy.