Revenants and Vampyrum have a lot of similarities. Both usually having red eye color, feed off of blood, superhuman abilities, and more.

However there are differences that make them different, not all revenants can turn invisible, form wings, and other similar abilities. Depending on their blood code will decide what abilities they are equipped with.

Like for Bell is shapeshifting and adapting.

Valentina's blood code will be bloodbath allowing her to leech off someone or multiple opponents blood, and call upon a monster to help her fight.

Revenants also require human blood or blood beads to live off of. They can't really get much from animals unlike their vampyrum counterparts.

Revenants also don't form claws on their hands.

Lastly the major difference is how quick a Revenant loses control very easily. While vampyrum can last a while without blood, revenant can last about a day. After the 24 hr mark they start getting hungry, and if they lose a lot of blood in combat they will enter into a state of frenzy.

Once a revenants enters a state of a frenzy it's similar to a vampyrum losing control, but their blood code gets out of whack. Causing them to take the form of a beast usually.

Queen:

The Revenants have a queen and follow a monarchy rule.

Relationship with Vampyrums:

Revenants from their homeland are aggressive towards outsiders, and other vampyrums. This is due to little blood beads to go around. They usually try to run them off and prevent them from entering the city.

Rogue Revenants:

Bell is considered a rouge revenants, usually because he moves outside of their city. It doesn't mean he doesn't respect the Queen, but it does mean he needs to be her foot soldier.
They are more prone to go into a frenzy since they are away from their food source.