35 cards where the number of colors is 1 and the card types include “creature” and the full Oracle text includes “changeling”

Amoeboid Changeling (Lorwyn #51)
Avian Changeling (Modern Masters #6)
Cairn Wanderer (Commander 2020 #130)
Chameleon Colossus (Forgotten Realms Commander #153)
Changeling Berserker (Lorwyn #160)
Changeling Hero (Lorwyn #9)
Changeling Outcast (Outlaws of Thunder Junction Commander #128)
Changeling Sentinel (Morningtide #6)
Changeling Titan (Lorwyn #200)
Fire-Belly Changeling (Duel Decks: Knights vs. Dragons #51)
Game-Trail Changeling (Morningtide #123)
Ghostly Changeling (Modern Masters 2015 #83)
Gladewalker Ritualist (Kaldheim #392)
Graveshifter (March of the Machine Commander #251)
Guardian Gladewalker (Kaldheim #174)
Impostor of the Sixth Pride (Modern Horizons #14)
Irregular Cohort (Commander Legends: Battle for Baldur's Gate #696)
Littjara Glade-Warden (Kaldheim #182)
Littjara Kinseekers (Kaldheim #66)
Masked Vandal (Kaldheim #184)
Mirror Entity (Outlaws of Thunder Junction Commander #83)
Mistwalker (Kaldheim #68)
Moonglove Changeling (Morningtide #67)
Mothdust Changeling (Modern Masters #53)
Orvar, the All-Form (Kaldheim #70)
Realmwalker (The Lost Caverns of Ixalan Commander #250)
Shapesharer (Lorwyn #85)
Skeletal Changeling (Lorwyn #140)
Taurean Mauler (Foundations #633)
Turtleshell Changeling (Lorwyn #94)
Valiant Changeling (Commander Legends: Battle for Baldur's Gate #711)
Venomous Changeling (Modern Horizons #114)
War-Spike Changeling (Modern Masters #139)
Webweaver Changeling (Double Masters 2022 #164)
Woodland Changeling (Lorwyn #242)

Though this query has ended, its relics still slumber in New Argive.