Well, the best way to deal with Warlock's Orb is to use a creature ability. But if it's as overpowered as you say... Any ways to balance it? I still want it to retain its unique spell-stealing ability, though.
Technically you can't because of the spell stealing ability. Spell copying ability yes, Spell Stealing no.
If you increased its cost to the point that it would give your opponent a fair chance to play their spell without losing it then you would also price it out of actual play.
If you want to keep the ability, you need to make the trigger 100% so that the opponent can playout lures, and increase the cost from 5 to at least 9 putting it out of 1st and 2nd turn lockdown range.
I looked over this spell, and I thought about it like this:
Gives you a 100% chance to negate the next spell cast... *etc.*. The permanent lasts for
X turns. 'X' could most likely stay at '1', so that your opponent wouldn't be stupid enough to cast any spells while it's up and give you the card advantage. In addition, to Kael's suggestions of increasing the cost, if you don't like having a timer on the permanent, why not have it drain
quanta overtime, so that you can't play a whole bunch of these on the field simultaneously without a huge drawback to 'guarantee' a ~100% chance (if you're retaining the 50% of negation/stealing).
I just wonder how Zanz will feel about stealing
spells in comparison to permanents or creatures.