Oh this is going to be FUN with Scheming Symmetry

Notion Thief but for tutors. Definitely cool, I like that they made it mono-colored so it can be slotted into a lot of decks. It's interesting that it gets better the higher your playgroups budget/power level, since the strongest tutors tend to be quite pricey (Demonic Tutor, Vampiric Tutor, etc.).

I want to play this in response to someone activating a fetch land.

Also, this is absolutely evil with Maralen of the Mornsong.

I personally can't stand the card. It's outrageously broken, and Aven Mindcensor did not deserve to get so dumpstered by another color.

Have to agree with Mown (though I'd vote for Leonin Arbiter instead). As mentioned this creates a pretty strong lock with Maralen of the Mornsong in commander, and Im pretty sure Legacy--and possibly even Vintage--wouldnt mind locking their opponent out of fetchlands, tutors, recruiters, etc for the cost of one Dark Ritual and maybe an Entomb+Animate Dead.

The Maralen interaction might actually make Maralen usable: historically she's been a terrible choice because she benefits the table more than and before you so you'll be destroyed by the effect of your own commander.

Painter's Servant made Grindstone usable
Vizier of Remedies made Devoted Druid usable
I want to say Animate Dead made Worldgorger Dragon usable, but Im not sure which came first
Grand Architect made Pili Pala usable
Splinter Twin made Pestermite usable

I could go on, but the point is that a relatively broken interaction should not be excused on the account that it makes an unplayable card playable.