The current titleholder of most valuable Gengar of all time goes to the Japanese Masaki Promo Holo from 1999, which received a TAG 10 grade, and sold for $101,260 through Goldin
If you do need to slow down the deck, the most sensible thing would be to tone down the control elements
Depending on your decks composition, youll be left with more permanents than your opponent, and if youre behind its a way to catch up
Ghalta and Mavren is a great duo and an excellent addition to any token commander deck that shares its colors
Promo Cards are also generally (but not always) marked by a stamp of some sort on the right side of the image, as seen on the picture of Mankey above
Cards produced by Wizards of the Coast from 1999-2003 are labeled Wizards Black Star Promos , while cards from Nintendo of America from 2003-2006 are referred to as Nintendo Black Star Promos