Some can be game-winning monsters , others just provide immense utility to the deck
If an effect allows you to search your library for a card with mana value 4 or less, you can't find There // They're // Their
One cycle to note is the Bobbleheads
Omarthis, Ghostfire InitiateOmarthis, Ghostfire Initiate costs XX and has power/toughness X, and gets a +1/+1 counters occasionally
Witherbloom really needs to have both lifegain enablers and payoffs to work, and all of Loreholds decks, aggressive or Flashback oriented, need a specific set of cards to work well
We can look at Gaeas Cradle as an example of what would happen to the price of Tolarian Academy if it ever got unbanned