A card can be a little pricey and dead in your hand sometimes if it means that its incredible strength is going to make up for the fact you were clogged on three of them for a few turns
Even the cheapest serialized card, Kwende, Pride of Femeref is worth over $80, with more powerful cards like Ragavan, Nimble Pilferer listed around $1,500
Sorin of House Markov might start as a two-mana creature but can flip super easily to the much more powerful Planeswalker side after you gain a measly three life
Secondly, I love seeing cards Im not familiar with on the opposite side of the table
Tekuthal, Inquiry Dominus Tekuthal, Inquiry Dominus takes each instance of proliferation and doubles it, making it very effective for quickly ticking up planeswalkers loyalty counters, opponents poison counters, and whatever else you need