#6 Charizard VSTAR SAR (~$63 / 6,500) Any set with a Charizard chase card holds long-term collector interest
A given white-blue-red deck, any number of blue-black-red decks, and, let's face it, any number of blue-red decks in general, all want this sort of effect
Elesh Norn, Grand Cenobite, Avacyn, Angel of Hope, and Moonshaker Cavalry each need just a small handful of creatures to potentially win you the game
If the copied creature has in its mana cost, X is considered to be 0
After you've narrowed down exactly which cards you need you can search for them either by looking through a deck template or even name searching for the card you need on the deck builder screen
Cards from 'The First Chapter', 'Rise of the Floodborne', 'Into the Inklands', and 'Ursula's Return' are not legal in the game's Core Constructed format, except when the card has been reprinted in a later set