Theres a pretty wide range for how to make a proxy. Some people write the name and abilities on a piece of paper covering a reversed card in a sleeve, some write the name of a card on the back of a bulk card like a basic land, and many people just print out the card in question
Building a mono-green deck around this is an easy way to cheat huge creatures onto the board, with the likes of Ghalta, Stampede Tyrant offering even more value for their entry
Each 61 card deck contains 1 random reverse holographic, meaning you could pull the Charizard
Looking for Shaymin prices and values
Additionally, Wizard from Beyond doubles up on ability triggers
As most lands are colorless, in most cases the resulting land creature will also be colorless