Vesperlark --> Mentor of the Meek
Murmuring Mystic --> Whispering Wizard
Night Clubber --> Nekrataal
Oona's Gatewarden --> Far // Away
Stun Sniper --> Honored-Crop Captain
Vesperlark was meant to support white aggressive decks in both pressuring and creature/card advantage, but an evasive creature with a leave effect ended up being awkward in play. Mentor provides the same advantage at the same CMC while also being grounded.
Murmuring Mystic and Night Clubber ended up being absolute hosers against other archetypes. The former was too fat and had too valuable of an effect and as such would outcompete other midrange or halt aggro while being difficult in many cases to get rid of. The Latter was simply too strong for a peasant cube with many X/1s and X/2s and could often act as a one-sided wipe or too advantageous of a combat advantage. Whispering Wizard provides the same Mystic value while being easier to remove. Nekrataal provides a classic, pressuring creature removal that is more limited to play than blitzing clubber.
Finally, Oona's Gatewarden and Stun Sniper ended up being rather lackluster and unexciting picks for all of their respective colors. Gatewarden is being replaced with a fan favorite fuse card that is great used only on either side and Crop-Captain takes a seat next to the well-liked Accorder Paladin.