Call the Spirit Dragons Better Call Saul, but for dragons: Call the Spirit Dragons, from Tarkir: Dragonstorm , is what you go for when an army of flying lizards isn't enough to win you the game
While the power buff is random and wont be consistent, it shouldnt be too hard for an equipment-based voltron deck to reliably draw a card even if the dice gods arent favoring you
In official tournament settings (sanctioned DCI events), proxy cards are not permitted
Other Foreign objects/materials: Pretty much anything can get stuck to the surface of a sheet
The familiar dimensions also make them a staple in tournaments, ensuring that everyone is on the same playing field
If these were one niche card that changed any card or spell into any color, itd at least be tolerable