What exactly does the power core do? Does it just shut down enemy scorestreaks?
To my knowledge, according to a calling card, it destroys any scorestreaks that are active during the time of deployment (the extent of which I'm not sure, I doubt that it'll instantly destroy a mothership, but that's how it worked in BO2 when an EMP could destroy a VTOL Warship), screws up their HUD really badly (if they're not using hard wired), and makes thrusting almost useless.
Edit: Zombies IS fun! Super fun, in my opinion. You just need to learn exactly what to do and what not to do in order to last more than a couple of rounds.
Edit 2: @TimeEffect, the Sparrow can kill anything as fast as the Annihalator, roughly. The only disadvantage is that the Sparrow's arrows have travel time while the Annilator's bullets are instantaneous.
The Scythe is probably the best Specialist weapon in the game (alongside a well used Ripper). It only needs to be wound up when hipfiring (that's the advantage and disadvantage, when hipfiring you can sprint and shoot but it must be wound up). However, if you aim with the Scythe, the bullets come out instantly (the disadvantage being severely limited movement).
Best map: Hunted, Stronghold, Combine, Evac
Worst map: Redwood
Also, sorry that I haven't responded to you about the handling 2v1s, I have the gameplay but I haven't had time to upload.