Ignited Revenants are a creature that is found within the Cataclysm mod. They aren’t bosses but are still extremely powerful. And killing them is required if you want to summon the Ignis, which is a boss.
Where to Find Ignited Revenants
Ignited Revenants can be found within the Burning Arena, a vast dungeon provided by the Cataclysm mod. To find the Ignited Revenants, you must enter the Burning Arena and head down a staircase to the floor below.

In each Burning Arena, just two Ignited Revenants will spawn. And they don’t respawn either, so if you want to kill more in the future, you’ll need to find a new Burning Arena.
If you can’t find the Burning Arena, you can use the command /locate structure cataclysm:burning_arena for Minecraft 1.19+, or /locate cataclysm:burning_arena for previous versions.

You can also craft the ‘Eye of Flame.’ This requires an Eye of Ender, 2 Netherite Scrap, 3 Soul Sand, and 3 Blaze Powder. When holding an Eye of Flame, you can right-click while holding it in the Nether to release it. Then, it will fly towards the Burning Arena, giving you an idea of what direction to travel.
Defeating the Ignited Revenant
Ignited Revenants look a bit like the Blaze. However, they’re much more extensive and a lot more powerful. Firstly, Ignited Revenants are surrounded by shields, which they can use to block attacks. In total, they have 80 health and 12 armor.
While bringing a Bow and Arrows might sound like a good idea, an Axe or Sword will be the best way to defeat them, and you should consider enchanting them beforehand, as the Ignited Revenant is very powerful.

During the fight, there are multiple ways that the Ignited Revenant will attack you. Firstly, they will charge at you while spinning their shields, which deals damage and knocks you back. This is relatively easy to tank, provided you have strong equipment and food, such as Golden Apples.
There are two different special attacks that Revenants might do. First, there is Ashen Breath. When the Ignited Revenant stands still, it might fire smoke toward you, and if you’re too close, it will blind you while dealing a bit of damage. Again, this is easy enough to tank.

While standing still, it might summon a Bone Storm instead. Bones will fly from the Ignited Revenant when that happens, hitting players nearby. After these attacks, you have a few seconds to retaliate, deal damage, and potentially remove some shields that circle the Revenant.
Drops
After defeating the Ignited Revenant, it will drop Burning Ashes. Back upstairs on the main floor of the Burning Arena, you can use these Burning Ashes on the Altar of Fire located in the middle, which is the only way to summon Ignis.

Defeating the Ignis isn’t easy, and it’s probably the most challenging boss within Cataclysm. So don’t summon Ignis unless you’re really prepared. If you need more Burning Ashes in the future, you should search for more Ignited Revenants within other Burning Arenas.