Advent Beasts are mirror dimensional beasts that cause travel the worlds. As the any Vent Riders used their Contract Card, it can befriend to their users so they can used it in battle.
Dragoonia is the first type of Advent Beasts who lives on the cities. Samuel Nakaoka named it Dragonizar who was tamed by himself as bonds.
- Unlike Ryuki Rider, they were not created from Samuel's Erase Card and Yuki's drawing. Because of Power Rangers: Vent Knights, they were smaller than it's counterpart when they were big. Although Sentai counterpart summoning the Mirror Monsters, they were stayed with the Riders when they used the Vent Cards.
- It was also shown Advent Beasts just retreats back to their partners' signature CallVent Cards rather than killing them by evil Rider who using the forbidden Exced Card and attempt to kill Samuel's rightful partner or revived them.
- In Ryuki Rider; it's Super Sentai equivalent, the Mirror Monsters fight the enemies along with their partners. However, the Riders does not fight with used weapons and finishers rather fighting techniques, this only Advent Beasts is only series mostly fight against them as the Riders used their weapons and finishers does so.