Mine Is the Only Truth The best use from Mine Is the Only Truth is if you run some kind of combo deck or spellslinger deck
That said, it is probably narrow enough that its power level wont become a problem and the fact that it needs other cards to make it truly broken should make it just a solid EDH card rather than a real issue
In the case of Muldrotha, if our important cards are 5cmc, we want our ramp cards to be castable on turns 1-3 so we can play our engines a turn early

Gloom - 002/190 (Mirror Holofoil) #2None $0.46 Charmeleon - 026/190 #26None $0.16 Paldean Tauros - 027/190 #27None $0.10 Pineco - 008/190 #8None $0.06 Scovillain - 021/190 #21None $0.10 Staryu - 038/190 #38None $0.13 Meowscarada ex - 014/190 #14Double Rare $0.31 Oddish - 001/190 #1None $0.13 Capsakid - 020/190 #20None $0.07 Koraidon #119Rare $0.12 Koraidon #124Rare $1.58 Koraidon #119Rare $0.18 Koraidon #90Uncommon $0.04 Koraidon #116Uncommon $0.08 Koraidon #8Promo $0.46 Koraidon #69Uncommon $0.10 Koraidon #122Common $0.25 Koraidon #52Rare $0.19 Koraidon #45Uncommon $0.28 Paldea Collection [Fuecoco/Koraidon ex] $56.74 Paldea Collection [Quaxly/Koraidon ex] $58.55 Paldea Collection [Sprigatito/Koraidon ex] $72.45 Paldea Collection [Set of 3] (Koraidon ex) Paldea Legends Tin [Koraidon ex] (International Version) $45.68 Paldea Legends Tin [Koraidon ex] $38.29 Deluxe Battle Deck [Koraidon ex] $25.66 Deluxe Battle Deck: Miraidon ex/Koraidon ex [Set of 2] $56.41

As Pokdex entry #859, its part of the Galar region's new wave of Pokmon, making its debut in Pokmon Sword and Shield
And while were talking about rare Pokemon merch, check out all of the exclusive items that were only available for sale at the Pokemon Center at the Pokemon World Championships 2019 that took place in August