Gimbal, Gremlin Prodigy is clearly the more unique of the two, requiring a specific deckbuilding strategy we've never seen before, but the payoff is lackluster in my opinion when compared with similar commanders like Urza, Chief Artificer
The effect isn't quite as interesting, but it's hilarious to note that the chicken is 3/3, which is stronger than some knights in armour in M:TG land, and it has the potential to grow even stronger when you roll a die
Some people thought that the card loss was too big a drawback, but you don't hear those people drawing first in constructed very often
Rebound: A Brief Overview The Rebound mechanic was initially introduced in Rise of the Eldrazi back in 2010
It enters the battlefield and lets you discard a card (ideally Vivi Ornitier) and draw a card
The reason for its rarity is that its a holographic card that has an error known as Shadowless, which means that its missing a shadow on the right of the cards image thats typically present in the base set holo