EDIT : well okay my Idea had more weak Spots than i expected , scroll down to see a awesome Idea by Awikun
First off :
This is NOT the ultimate Solution since you still gonna need some Manpower to take out a Multibox but it will give you a better fighting Chance and add new Tactics to legit Tower-PvP as well.
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Idea behind :
What makes a Multibox so deadly besides the sheer Numbers 1 Player can bring into Battle ... the Ability to focus Specials/Perks/Pets& Nukes.
The Idea :
A unresistable Nano that forces both the Caster and his Opponent to fight eachother for 15 to 30 seconds .
The Nano can only be cast in Zones with 25% or less Supressiongas .
The Nano can be cast upon your own Faction only in 5 % and 0% Gas.
The Nano cannot be cast upon yourself , your Teammates or your Raidinterface .
It disables targeting anything other than himself and the engaged Enemy and the Ability to zone/grid/beacon for both Toons involved.
Both are still attackable & healable by anyone else , if they use AoE-Effects it still hurts/heals/buffs/debuffs .
The Nano cannot be overwritten or refreshed and both Fighters gain Immunity afterwards for 15-30 Sec.
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Impact :
A dedicated Team of twinked up Toons could engage a Multibox and pretty much fight each Toons seperatly.
Scripts no matter how advanced cannot make up for a good Player in a 1 on1 Situation , the "Hunters" should have a good chance of taking out the Multibox if their Toons and Playstyle are good enough.
The Multiboxer still has the "Teammates" he paid for and will recieve Blockers , be able to use BGH etc....
The Nano could be used to temporarely disable a Targetcaller / Doctor from doing his Duty.
The Nano could make lesser geared People who dont care about reclaiming important if they sacrifice themself for the Benefit of their Side.
Funcom could reverse the Changes to /assist and Meeps IF after a Period of testing this Idea proves to be practical.