Magic: The Gathering's planeswalkers are a well-known card type first printed in Lorwyn. Since then, planewalker cards have been printed in a plethora of sets. Originally, planeswalker cards had three loyalty abilities with varying effects. Over time, planeswalker cards changed to include static abilities and up to four loyalty abilities.
In my recent TCGplayer Infinite article, 6 MTG Planeswalker Cards You Should Be Playing, I highlight six planeswalker cards worth consideration in the 99 of Commander decks. Recent sets contain a handful of planeswalkers with abilities that synergize well with certain Commander Deck strategies and themes. You should read the article to see if there is a planeswalker that could improve the power level of an existing or new Commander deck.
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