Let me start with the 1st edition version of the set, which although not too hard to find were pretty short-printed as well: The 1st edition version of this set was only available for purchase online On top of that: it was only available for a two week period (June 15th to July 1st, 2007) On top of that: it could only be bought by Japanese players On top of that: it was TCG-wise a pretty bad set, so not a lot of players bought it On top of that: it was released near the end of the TCG season, so they could only use the few usable cards for little over half a year, before they were out of rotation again On top of that: the Seviper is a Rare, and unlike a lot of other sets, the non-Holo Rares had the same pull rates as Holofoil Rares, ex Ultra Rares, and even the Jolteon/Vaporeon/Flareon gold stars On top of that: Seviper isnt a very popular Pokmon to collect, so less likely to be put up for sale than the Pikachu This information above is for the 1st edition version, though

Cards like Nightmare Unicorn can use their effects during the opponent's turn as a form of disruption and cards like Avramax become almost impossible to get rid of for most decks
I often find my first activation is just using two spare-ish mana to turn this on and grow it without getting an attack in, just a kind of way to prime it for an efficient attack later
This makes it one of the rarest cards on the planet
Turns out this new common Summon has a lot to offer in the format, meaning it could see some serious play there when alls said and done