What it does
"Symphony of Pain" isn't an official Magic: The Gathering keyword or evergreen ability—it doesn't appear in the comprehensive rules or on any printed card. It may be a custom/homebrew card name, a misremembered ability, or flavor text someone encountered, but it has no standardized rules meaning.
If you saw it on a specific card, check that card's actual reminder text or oracle wording, since the real mechanics will be spelled out there. Common abilities people confuse with invented names include things like "ping" effects, damage triggers, or punisher mechanics, but none of those is called Symphony of Pain.
For accurate rulings in your Commander game, look up the exact card on Gatherer or Scryfall—those give the official, tournament-legal text. If it's a custom card, ask whoever made it how they intend it to function.
