It can deal an explosive amount of damage, and under the right circumstances, win the game in just one attack while your opponent is at full life
Look at that Laser Blade attack, 1 Energy card for 200 damage
Neither player can activate the effects of the equipped monster while you control it
However, her effect also prevents your own Cards from targeting the Melodious, even if most of the archetypal ones are unused
This means, that the cost of activating the ability (1 colorless energy) is meaningless if the rival has an ability that costs 3 energy (from any type), as Ditto won't be able to use the attack, and will waste its turn doing basically nothing
Bartz Klauser (Winota, Joiner of Forces) Magic has a very small number of commanders I dont think you can build fairly without resorting to playing Draft chaff, and Winota, Joiner of Forces is near the top of the list