Death Sword Art
Deals damage to 3 units in your team. His basic attacks are usually not an issue, but he can quickly kill your units with them if you get stunned with his Ultimate.
Earthquake
Inflicts damage to everyone in the team and stuns them for 4 seconds. The damage is not an issue, but this 4-second stun paired with his Massacre passive is really dangerous.
You can freeze / root / fear him or use units like Galahad to avoid this stun.
Massacre
Every time Death Lord kills anyone, his attack increases by 50%. This can be lethal on a lot of situations and can lead to a full wipe pretty fast.
Bring damage reduction units and/or healers to avoid this passive from procing.
Knockback Immunity
A passive you don’t have to worry about at all since we barely have any units in the game that can move bosses.