18 cards where the text includes “changeling” and the card types include “creature” and the color identity ≤ BU and it’s legal in Commander

Amoeboid Changeling (Lorwyn #51)
Barkform Harvester (Bloomburrow #243)
Bloodline Pretender (March of the Machine Commander #350)
Cairn Wanderer (Commander 2020 #130)
Changeling Outcast (Outlaws of Thunder Junction Commander #128)
Ghostly Changeling (Modern Masters 2015 #83)
Graveshifter (March of the Machine Commander #251)
Littjara Kinseekers (Kaldheim #66)
Mistwalker (Kaldheim #68)
Moonglove Changeling (Morningtide #67)
Mothdust Changeling (Modern Masters #53)
Orvar, the All-Form (Kaldheim #70)
Shapesharer (Lorwyn #85)
Skeletal Changeling (Lorwyn #140)
Three Tree Mascot (Bloomburrow #251)
Turtleshell Changeling (Lorwyn #94)
Universal Automaton (Modern Horizons #235)
Venomous Changeling (Modern Horizons #114)

It is the moment of discovery, the triumph of the mind, and the end of these results.