Q. Can I use Reuniclus' Damage Swap to move 6 damage counters onto my Solosis all at once, and then it gets Knocked Out?
A. No. Damage Swap's effect does not involve you moving multiple damage counters at once - you are moving damage counters one at a time, and each time you move 1 damage counter, you are using Damage Swap exactly 1 time each. As soon as that 3rd damage counter will hit Solosis, it is knocked out instantly, and your opponent takes a prize card.