While it's legal in Modern, Commander, Historic, and Vintage, Sauron's Ransom seems to be gaining in popularity for Legacy players
Kokusho, the Evening Star - A 5/5 flying creature that happens to have a really nasty death effect, serves as an excellent attacker, blocker, and sacrifice target

Sword & Shield Theme Deck [Rillaboom] $17.30 Galar Partners Tin [Rillaboom V] Galar Partners Box [Rillaboom V] $202.99 Galar Partners International Tin [Rillaboom V] $83.00 Legends of Galar Tin + Galar Partners Tin 2-pack [Zacian V/Rillaboom V] (Retail Exclusive) $179.99 Legends of Galar Tin + Galar Partners Tin 2-pack [Zamazenta V/Rillaboom V] (Retail Exclusive) Fusion Strike Premium Checklane Blister [Rillaboom] Crown Zenith Pin Collection [Rillaboom] $78.08 Rillaboom #13Holo Rare $0.30 Rillaboom #SV6Shiny Holo Rare $3.18 Rillaboom #18Holo Rare $0.27 Rillaboom #14Rare $6.51 Rillaboom #16Uncommon $0.16 Rillaboom #10Uncommon $0.11 Rillaboom #8Rare $0.28 Rillaboom #84Ultra Rare Rillaboom #7Rare $0.50 Rillaboom - 008/190 #8None $0.31 Dedenne #SV51Shiny Holo Rare $6.01 Sobble #SV25Shiny Holo Rare $2.06 Drizzile #SV26Shiny Holo Rare $4.71 Frosmoth #SV34Shiny Holo Rare $3.92 Hatenna #SV54Shiny Holo Rare $2.97 Milcery #SV57Shiny Holo Rare $6.20 Morpeko #SV44Shiny Holo Rare $18.41 Blipbug #SV7Shiny Holo Rare $1.79 Snom #SV33Shiny Holo Rare $6.33 Galarian Darmanitan #SV24Shiny Holo Rare $1.69

The modern-day commander decks are genuinely better, in my opinion
The main point of polymorphing is to target your own stuff, and this blue instant wants you to pray and hope you deal with an opponents creature without flipping them into something even worse
GX cards introduced GX attacks , special attacks you could generally use only once per game (youll see (You cant use more than 1 GX attack in a game.) style text on the card)