It can swarm the battlefield with Urza's effect and turn all your artifacts into mana dorks to pay for both Urza and various spells easily
Is Madness at Instant or Sorcery Speed
It only costs three mana for a 2/4 and comes with both of these solid abilities, making it a staple in elf and reanimator decks
Derevi, Empyrial Tactician Derevi, Empyrial Tactician has one of the most absurd abilities in the game, ignoring commander tax by entering from the command zone for 4 mana every time at instant speed
However, Cavalier is much better than Grey Knight thanks to its ability to destroy any nonland permanent instead of just attacking creatures
For example, say you've cast two spells this turn, and with Murmuration's last ability on the stack, you cast a Blizzard Strix (a Bird creature spell with flash that may have been chosen for this example due to being an adorable owl)