Exdeath, Void Warlock is the perfect card to help a black/green deck stay alive long enough against aggro decks to put together all of its synergies
Notice the weird spacing in the text on the counterfeit card
In Timeless control builds, its synergy with cheap cantrips and steady draw makes flipping it quick and lets it dominate games with relentless card advantage
Minwu, White Mage would also be a must: every time you gain life, she puts a +1/+1 on each cleric you control
While some colors may excel at Voltron strategies more than others, Voltron is one of the few archetypes that can function well in nearly any color identity, with each color bringing an additional flavor to the Voltron pie
These aren't just the most obviously "broken" cards (some might not have a home yet) but they all stand out as strong contenders for future competitive decks, either in Standard or beyond