If you are using newton units, you will need a laser beam like on LLTs, not the current newton beam impulses like Heat-Rays.
This beam should also affect your own unit.
It needs a very heavy unit with a lot of HPs and very high metal costs, to avoid 90% of the gravity effect and damage.
There should also be some option to let newtons keep a unit in range but don't attract it more than 10% of maxRange.
Like a tractor beam which keeps enemies attracted, but don't let them get into fire range.
Or add some EMP damage to the attraction and let it attract the enemy up to 80% and pull it back if it is getting to close and is a danger for our own unit's HPs.
1000 metal for the EMP+Attraction - would it be fair?
Notice that it can only imprission low-cost units, not stuff like sumos/dantes.
But than it would be similar to dominatrix, except the damage the other unit takes from the gravity effects.