Choose 1 of the Defending Pokémon's attacks. Copy copies that attack. This attack does nothing if Mew doesn't have the Energy necessary to use that attack. (You must still do anything else required for that attack.) Mew performs that attack.
Extra Draw
If your opponent has any Pokémon-ex in play, search your deck for up to 2 basic Energy cards and attach them to Mew. Shuffle your deck afterward.
How much is Mew δ #3/17 worth?
Mew δ #3/17 is a Rare card from POP Series 5 (2007) — today it trades at roughly $418.33 ungraded. Across the 2 printings we track, copies run anywhere from $441.10 to $1,499.99 depending on the version you're holding.
Grading changes the math on this one: a PSA 10 is valued around $7,924.76, roughly 18.9x the raw price, while a PSA 9 sits near $6,441.38. 701 copies have been graded to date, and 1% of them came back a 10 — worth knowing before you pay grading fees.
These figures come from nightly market-data syncs verified against completed sales. Use the chart above to see the trend before you buy or sell.