As of my count, there are 8 different card types: land, creature, sorcery, instant, artifact, enchantment, planeswalker, and battle
The trickiest part about drafting Grixis is balancing all three, and theres no easy way to determine which is the most important at any given time
If you want to be the bad guy and have one of Magic's most infamous scumbags helming your deck, this is the card to look at
Obviously, if you have graveyard synergy, flashback, or cards you want to discard, the effect is all upside, but you don't have to go this far
Myr offer a generally low casting cost for these decks coupled with the two most common myr modes: mana production, and combo synergy