You must choose two targets
Generally, playing these means youre base RG or GW, as those colors have most of the summons
We spent the first ten plus turns amassing a magical army, where one players field usually consisted of 2x Doppleganger, 3x Mahamoti (one with Invisibility) and a Merfolk Assassin on one side, standing watch against the other players field of 3x Nightmare, 2x Royal Assassin and a Lord of the Pit with a Breeding Pit somewhere in play with two swamps permanently tapped underneath it
These products were not Standard legal
Still, the Dash ability of Ragavan, Nimble Pilferer means that it is a constant threat that your opponent needs to be aware of, and that in it of itself is powerful as it will force your opponent to sequence in such a way to respect the potential Dash attack
Otherworldly Gaze If you count Surveil spells as self-mill (and I do, given how rarely you see triggers that care exactly how cards end up getting from your library to the graveyard), then Otherworldly Gaze is as good a choice as any for the most consistent, efficient, no-bells-and-whistles version of the effect