What it does
"Death Ray" isn't an official Magic keyword or ability—it's not something printed on cards or defined in the comprehensive rules. You may be thinking of a custom card, a joke reference, or confusing it with an actual effect.
If you mean a card that deals damage to destroy a creature, that's just standard targeted removal (like "deal X damage to target creature"). The real rules nuances there involve damage versus destruction: damage-based removal can be dodged by indestructible, by regeneration (which doesn't stop damage but prevents the resulting destruction), or by toughness-boosting tricks, and it won't kill creatures with hexproof or protection from the damage's color.
If "Death Ray" is from a specific set or homebrew context you're referencing, let me know the exact card text and I'll explain how it functions in Commander.
Iconic cards with Death Ray
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