Any creature with two or more abilities is desirable, but especially those that have utility outside of being eaten by Soulflayer
A blue Background is your best bet with Wyll since this will grant access to some other powerful dice-rolling effects like Pixie Guide
The Lightning-type Pikachu & Zekrom- GX is a powerhouse card, capable of searching up Energy and striking multiple Pokmon
However, this low damage output is easily mitigated by the Dusknoir engine , as these cards have powerful abilities that can make it easier to knock out the opponent's Pokmon in one attack
Im taking a more holistic approach, considering a legends raw power, its impact on the format, its enduring popularity, and the uniqueness of its design
Perhaps thats why Norns got the fan club she does