There is an obvious synergy is with an artifact creature called Pentavus and another even older artifact called Ashnod’s Altar. With Pentavus, you remove a +1/+1 counter from it for a single colorless mana to make a token. You then sacrifice it with Pentavus’ second ability, then a +1/+1 counter is placed on Pentavus and you can repeat the process. However, you can only do this for as much mana as you have. Using a sacrifice outlet like Ashnod’s Altar with that token instead to create 2 colorless mana not only lets you get as many tokens as you’d like, but you can also get infinite amounts of colorless mana, as well.
There’s also a cool interaction with Mazirek and creatures with Persist. While you need an sacrifice outlet on board, as well, being able to reuse creatures like Puppeteer Clique and Woodfall Primus is powerful. Because creatures with Persist come back into play with a -1/-1 counter, you can put Mazirek’s +1/+1 counter ability on the stack and counteract that -1/-1 counter. If you have the sacrifice outlet, you can literally reuse Persist creatures as often as you like. Having Primus machine-gun every noncreature permanent of your opponents is pretty mean, but it’s been done before with the Undying ability - the opposite of Persist - of Mikaeus the Unhallowed.
With how many creatures and Enchantments in Green and Black that give you benefits from sacrifice, Mazirek should be a very effective Commander and will find homes in many Green/Black/X decks. Savra, Queen of the Golgari is a great friend for Mazirek, as in the right combinations you can force opponents to sacrifice all of their creatures or gain infinite life, or both! There are many existing Commanders that would be happy to have Mazirek in their 99. Shattergang Brothers, a Commander who is all about sacrificing permanents, would definitely enjoy Mazirek helping him and his forces out. but this Death Priest could make a fantastic for Insect Tribal, Infect, or your traditional “goodstuff” Golgari deck based around benefiting from sacrifice. With all of the cards in Battle for Zendikar that benefit this archetype, such as Smothering Abomination, this should be a really fun Legendary Creature to build around.