In short: The most valuable Magic: The Gathering cards are driven by a combination of power and scarcity, with the Alpha printing of Black Lotus historically topping the list
The main reason Arcane Denial is so good is that it helps your deck get to where it wants to be while simultaneously stopping your opponents deck doing exactly what it wants to do regardless of what that might be
If it wasnt a collectible from that particular IP, I think itd be cheaper, but that is the only special version until now
Tax-like effects that require payments other than mana, like the effect of the first ability of Sivitri, Dragon Master, aren't taxes for the purposes of Tax Taker's ability
1: Put a +1/+1 counter on each creature you control
Id love to get my hands on a few, but I honestly dont know if I could stop myself from opening them