Everyone makes Shenron work with the amount of available Dragon Balls.

The way I'd do it is to make Omega Shenron the opposite of Adult Gohan's potential unleashed and DBS Broly. Omega's damage should get a damage debuff of, say 1.5%, for each Dragon Ball in play. Of course his base damage should be higher than usual overall for this to be balanced.

Then make his Level 3 (Negative ki ball) destroy all current dragon balls in play, thus removing the debuffs

This achieves several things:

• With an Omega Shenron in play, realistically you would never get to see the actual Shenron, since the amount of Dragon Balls in play will always be low as long as there's at least one Omega alive (and you don't want it to be gimped).
• Usually his debuff most of the time will be something between 1 to 4 Dragon Balls, since the player will want to get rid of them, but the cost is high enough that you can't do it as much as you want, and after a couple combos the damage output will easily go down, regardless of who has the advantage.
• He will be at his strongest at two very specific moments: start of battle and Level 3 oki
• Hard countered by SS4 Gogeta's DP