Popularity: Charizard is one of the most popular Pokmon, enhancing its desirability among collectors
Mana Most of the mana engines have been alluded to already, with the cost-reducers teaming up with Senseis Divining Top and the Krark-Clan Ironworks teaming up with the artifact regrowth effects
Killing them isnt enough, as players just need to chain cheap spells to resurrect them from one turn to the other, and conventional removal spells like Fatal Push just don't cut it to deal with them
If you play the Seriema on turn 3, Anticausal Vestige can single-handedly Station the Seriema on turn 4 (plus its other leaves-the-battlefield triggers)
Some cards can have a pull-rate as high as 1 in 100 packs
The first Charizard GX card featured Crimson Storm, still with the colossal energy cost and with the setback of having to discard 3 fire energy if you use Crimson Storm