Paying six mana for that effect is atrocious, but Soul Spike has an alternate casting cost - you can exile two black cards from your hand instead of paying its mana cost
As this article is being written, Disney Lorcana: Reign of Jafar has only just been released to local hobby stores and other select retailers and has not yet become available at mass-market retailers
Lets demonstrate this by taking a look at a fairly average Sealed deck I recently played that had 17 lands: Why is this deck playing 17 lands rather than, say, 16 lands (-1 Forest, +1 Arrogant Poet) or 18 lands (-1 Tenured Inkcaster, +1 Swamp)
When he gets staked, he gets to have a nap in his coffin, turning into an artifact that pops out 1/1 vampire tokens (not sure how they all fit in that thing) for three turns, then transforming back into his creature form
As newer packs come out and older ones increase in rarity, even the most recent Charizard cards will likely grow substantially more expensive
When viewing the rules text of cards like these, it can be easy to forget that Bloodthirsty Conqueror is also a 5 mana 5/5 Flying threat with Deathtouch, which is an excellent rate even for a Mythic in black