My main is an arcane specced mage. I haven't lost to a single shaman 5boxer in any BG and I can usually take any of them alone. I dump trinket, arcane power, icy veins, troll berserking racial so that my GCD is only 1 sec. Arcane-specced arcane explosion has MASSIVE crits and critical strike chance. (Clearcasting is also almost a guaranteed crit). I fire ward, blink inside them, frost nova so they can't move. If they trinket out of the frost nova I cold snap and frost nova again. (40/0/21 spec). I can kill any shaman 5 boxer in a few seconds, using PvE gear. I've had a few boxers leave the BG in anger because one stupid troll AoE's them to death.

This is of course, only if I can get to them alone. They tend to work alone though, since especially in maps like AB and WSG even clueless teammates tend to spread out more and avoid being near him, seeing that the 5 boxer is actually one person using 1/3 or 1/2 of the team's entire resources in one place. My mage has a grand total of 23 resilience and 7.5k hp, but with 1.2k spell damage and around

Really, people have no choice. Trying to CC, fear, or nuke down a shaman multiboxer individually is impossible. The only way to do it is to jump inside them and spam AoE.

Note: this is when I'm 1 boxing vs. a 5 boxer. My clones haven't seen 70 BG's yet.