Jegantha, the Wellspring

The companion restriction here is the loosest in the cycle, and that is the whole story of why it became a problem. "No repeated mana symbol in any single card's cost" reads like a real deckbuilding tax, but most competitive decks already lean on cards with hybrid, generic, or single-pip costs; the requirement quietly excludes double-colored spells and little else. That gap turned Jegantha into a nearly free addendum for a huge swath of decks: an eighth card in hand for three mana, with a five-color mana ability stapled to a 5/5 body that could pay for whatever the deck was actually doing. Companion was designed as a covenant, a build-around promise you honored for a payoff, but this one asked for almost nothing while handing over card advantage no other card in the game grants at zero opportunity cost. That imbalance is why the mechanic as a whole was reined in with a rules change that made every companion cost three mana just to move it to hand, and why Jegantha specifically drew bans in the formats where its restriction was trivially met. The mana ability itself is honest enough (it cannot pay generic costs, so it is not a Rituals engine), but the card's legacy is a case study in how a companion condition that fails to constrain becomes a constraint on the format instead.