Subtly has (slow) cycling despite an empty board. Neat. Intended?

Entirely. It does so little that adding "up to one" felt necessary for the versatility.

In case this ever comes up: If you choose to cast this with a target and that target is removed, the spell is countered and you won't draw a card (comparable to Expose Evil Card FAQ).

I'm trying to make a card that can overcome this wrinkle for a specific case and thought pointing this out may be useful.

It shouldn't be countered. That's why the abilities are separate, and one of the functions of the up to clause.

What rule does that?

Rule 608.2b. If there are targets and all of the targets are illegal, the spell is countered. There's no way around it

The "up to" clause allows you to cast the spell without targets (in which case it does not get countered for all its targets becoming illegal), but if you choose a target nevertheless, then making that target illegal will counter the spell as a whole.

I cannot for certain tell you which rules the Rulings intend to reference, but these three seem relevant:

> "114.6. Spells and abilities that can have zero or more targets are targeted only if one or more targets have been chosen for them."

> "601.2c. [...] Once the number of targets the spell has is determined, that number doesn't change [...]"

> "608.2b [...] If all its targets, for every instance of the word "target," are now illegal, the spell or ability doesn't resolve. [...]"

Anyway, the ruling is consistent e. g. Repel the Darkness Rulings:

> "6/15/2010: You may target zero, one, or two creatures. The creatures don't need to be untapped.
6/15/2010: If you target zero creatures, Repel the Darkness can't be countered for having no legal targets. When it resolves, all that happens is that you draw a card.
6/15/2010: If you target one creature and that target is illegal as Repel the Darkness resolves, the spell is countered. You don't draw a card.
6/15/2010: If you target two creatures and they're both illegal as Repel the Darkness resolves, the spell is countered; you don't draw a card. If just one is illegal, the spell does resolve; the remaining legal target becomes tapped (if it's untapped at that time) and you draw a card."

Almost every set has a card like this

> Almost every set has a card like this

Cantrips with targets? Yes. Cantrips that use "up to N target" in their wording? I think, I found bout half a dozen in the whole game.

And the interaction we are talking about is specifically about the more narrow subset, because it is about the card working differently depending on a choice you cannot make for most cantrips.

Formal logic systems are my bane and my salvation.