Binding Intervention et al.

[latviathan]

Binding Intervention
 
Instant
As an additional cost to play Binding Intervention, remove two lands you control and two
cards in your hand from the game.
Split Second
Until end of turn, target player can't play spells or activated abilities. Tap all permanents that player controls. You may counter target spell, activated ability, or triggered ability.


I really liked the white counterspells in Planar Chaos. Makes sense to me.
White, I think, as it expands its color pie abilities, is well placed to play around with losing resources, card disadvantage and tempo as a cost for expanded powers. Split second / uncounterability works well with the really big ones like this, so that the overinvestment won't lose you the game. To me, everything makes sense in context. I don't think you put these kind of things on commons, but for rares definitely there's room for it. Cards that you invest a lot of resources into and that very reliably do something you want or stop something you don't want seem very White. White could be thought of like the DCI - the color that can bring down the hammer and use an emergency ban.

[Harlequin]

This is hyper-cracked-Voidslime.

Its like "Think Voidslime, but rather than being 2 colors, is mono-white but costs 1 more colorless mana.  Oh and and they can't play spells or abilites before it resolves, making it basically counterable.  Oh yeah, and they can't play spells or abilites AFTER it resolves either. And why not tap everything they control... which will be hilarious because they can't respond.  Oh and if you don't have enough 4 open you can still cast it."


As worded, your "may" is in the wrong place.  As worded you cannot cast this without a target spell or ability.  The may choice is made on resolution.  So you can't just cast this at the start of thier upkeep or the begining of your turn because it won't have a target that you can choose to counter or not counter.  You have to word it like:
Choose one or Both - poop all over them; or Counter target spell or ability.  That way you could declare a mode with no target.

However I can't think of a situation where you would ever want to cast this without something to counter on the stack.  If they haven't played anything yet you can wait to see if they intend to play anything.  If they don't then you just sit on this.  If they do, you counter thier commitment and say 'no' for the rest of the turn.

This is probably closer to Split Second Timestop than anything else.  Timestop + Turnabout.