Many people think of the old-school precons like the Kaalia of the Vast and Edgar Markov decks as highly powerful
Production Foreshadowing: A few episodes of Daneboe's Angry Birds Let's Play provide possibly-unintentional examples, as some of them open with a (most likely unintentional) Freeze-Frame Bonus showing Daneboe's computer screen
Those monsters include Ghost Ogre & Snow Rabbit , Ash Blossom & Joyous Spring , Ghost Reaper & Winter Cherries , D.D
Not to mention, the ATK doubling lasts until your next Standby Phase, so it's not like her ATK drops to normal during the opponent's turn, allowing them to destroy her by battle
Vision HEROs Vision HEROs really let you see the potential in a HERO deck
Oblivion Sower and Blight Herder are good against delve and various spot removal