Plasma Incinerator isn't a keyword—it's a legendary artifact Equipment from The Brothers' War. It gives the equipped creature +3/+0 and the ability "Whenever this creature attacks or blocks, scry 2." More importantly, it has its own activated combat trigger: whenever the equipped creature deals combat damage to a player, you may have Plasma Incinerator deal that much damage to any target.
The nuance people miss: that bonus damage triggers off combat damage to a player, so it doesn't fire when your creature damages another creature. The redirected burn can hit any target—a creature, planeswalker, or another player—letting one connecting attacker effectively double-dip damage.
In Commander, it shines on evasive or unblockable creatures, turning a single hit into removal or extra reach. The scry on attack/block also smooths your draws, making it a solid value Equipment.