Not only does this Regent synergize well with the rest of the Abzan clan with which its aligned, it also is just very solid on its own as a Limited bomb. Its best interaction is with the Legendary Dragon from Fate Reforged, Dromoka, the Eternal. Dromoka has an ability that whenever a Dragon you control attacks, you get to bolster 2 - put 2 +1/+1 counters on the creature with the least toughness you control. These two attacking in tandem is quite powerful.
The Regent also has some sweet interactions with other cards that benefit from gaining life. Archangel of Thune, for example, allows you to put a +1/+1 counter on each creature you control each time you gain life. The Archangel and Regent being on the board at the same time could make opponents quite miserable. If you're looking to build around this strategy, there are a couple of other cards that work well with this lifegain, such as Ajani's Pridemate and Cradle of Vitality. The Archangel and Cradle are not in Standard alongside the Regent, but they can work together well in other formats.
In Commander, the Regent should find a home in any deck that likes +1/+1 counters and lifegain. It has a chance to become an absolute house in a multiplayer format, but it's strong enough that it could see some other Constructed play, as well. It's a solid Dragon that should find a home in a good number of brews.