As sealed inventory decreases, box and card prices tend to appreciate a pattern clearly demonstrated by OP-03 Pillars of Strength and earlier sets
Not something seen often in Magics history, but like most others that do exist, there is a limitation
On the front side, it forces everyone to discard when it enters or attacks, then it rewards you with card draw based on types discardedwhich often puts you far ahead
Use the characteristics of Spark Double as it enters the battlefield, not of the copied permanent, to determine whether it enters with an additional counter on it
On top of that, this card replaces itself and gives the creature flying, providing it with some evasion
its restrictive casting cost allows the designers to give it an enormous amount of power for a five mana card