How about a spell for DnD Next? How about a nice cantrip…
Self Doubt
Enchantment cantrip (mind effecting)
Casting Time: 1 action
Range: 60 Ft.
Duration: 1 round
Target creature makes a charisma saving throw. If it fails, it is racked with doubt. On its next turn all attacks and skill checks are made with disadvantage. If cast as a first level spell the target takes an additional -1 to the rolls. For every level cast above first, increase the penalty to the rolls by one.
Thoughts?
Throat Punch Games 
A bit overpowered for a cantrip especally since the DC goes up with all other DCs, and putting in modifiers ontop of the disadvantage is a bit redundant. I would add a different but just as powerful effect and make it a first level spell.
I was thinking of flare in 3.5. If it hits you don’t get an action.
I do agree it might be to powerful. Would just hitting and disadvantage as a cantrip be ok?