Whether it's among the most expensive cards in Darkness Ablaze or taking the crown for the base set's most valuable starter, Charizard is always desirable
While it does scale down in the late game, a three-mana draw-three in the early to mid-game is great, and giving your opponents cards with it might not even be bad, especially if you run effects that profit off of exactly this
Wherever you have gigantic, powerful creatures with wild abilities, you'll see demand
So you can sacrifice the Primus infinite times, generating infinite mana and blowing up infinite noncreature permanents in the process
Some are obviously better than others
The turn when you get to pull two or more phoenixes from your graveyard onto the battlefield attacking is usually backbreaking