Getting back a Devoted Druid with (effective) haste enables the deck to recover against removal and grind out longer games
Even without keeping your opponent from retreating, Arbok is still quite strong by itself

A Killer Among Us Acid-Spewer Dragon Acidic Slime Acidic Slime Aether Poisoner Aetherblade Agent Age of Ultron Agent of the Fates Agent of the Shadow Thieves Agent's Toolkit Ahriman Akroma, Vision of Ixidor Alchemist's Gift Alela, Artful Provocateur Alesha's Legacy All-Out Assault Alpharael, Dreaming Acolyte Ambush Viper Anhelo, the Painter Animus of Predation Ankle Biter Ankle Shanker Aphelia, Viper Whisperer Aragorn, Company Leader Archetype of Finality Archpriest of Shadows Argivian Avenger Arisen Gorgon Armed Assailant Arno Dorian Arnyn, Deathbloom Botanist Arvad the Cursed Ashnod the Uncaring Ashnod, Flesh Mechanist Aspect of Gorgon Assassin Initiate Astarion, the Decadent Atraxa's Skitterfang Atraxa, Grand Unifier Atraxa, Grand Unifier Atraxa, Praetors' Voice Aurora of Emrakul Aveline de Grandpr Aven Heartstabber Avenger of the Fallen Axebane Ferox Ayli, Eternal Pilgrim Baleful Eidolon Baleful Strix Bane-Marked Leonin Barrowgoyf Basilisk Collar Battle-Rage Blessing Battlefly Swarm Bebop, Skull & Crossbones Bilious Skulldweller Binding the Old Gods Bitterblade Warrior Bitterheart Witch Black Waltz No

For more ideas for Commander decks, check out our list of the best MTG commanders
Theyre a new kind of counter that help make some Phyrexian mechanisms stronger, and there are cards that help manipulate the number of them or where they are