Contrast this with Merfolk Branchwalker, where both options are good: About 40% of the time its sort of a Silvergill Adept
Behold the Power of Destruction destroys all of one opponent's nonland permanents
It can be transformed for seven mana, but one of those mana can be paid with either a single White mana or two life
When you get a good chump block or somehow draw removal with your Elder you get a nice juicy four for one
Using the earlier example of Mana Vault and Izzet Signet, a fast-mana deck under Rule of Law needs to choose between casting their mana rocks and casting the things that those mana rocks would normally allow them to, like interaction or threats
If Invasion was about combining Magic s five colors in creative ways, then a single card turned sideways and split down the middle to feature two spells instead of just one, was the perfect way to bring that theme to life