For example, a player can't activate the transmute ability of Muddle the Mixture if Pithing Needle naming Muddle the Mixture is on the battlefield
When you resolve Kiora Bests the Sea God, you get an 8/8 hexproof creature right away
While Gideon may not survive said attack, it can be a solid means of buying you much-needed time
Were still going to cover them here (loosely ranked from worst to best) so you know the best playable options available, but given the opportunity, leaning on another color and/or mana rocks when possible will usually yield better results outside of specific strategies
If you buy two, you and a friend can practice games together before you start attending events
Summary Grixis offers powerful card draw, control, and removal options for Commander decks