Nasty Plot doubles Special Attack, not Attack, so Bold is a fine nature to build Togekiss into a fantastic tank. With the IV's it has, a spread with 252HP/178D/64Speed/16Sp.A should do well. He will be able to outspeed most Rock types to take them out with Aura Sphere making Electric types his main concern however his defenses are stellar and he has a handy chunk of HP. He will hit 250Sp.A which is respectible enough to do a lot of damage to a lot of Pokemon, but after a Nasty Plot he will hit 500 Sp.A and should be able to OHKO anything that isn't as bulky as hell. Since you also will have Roost he can heal up damage and also buy himself a turn of not being weak to Electric and Rock.
So I need you to feed him 10 HP Up's, 10 Irons, 6 Carbos', and 1 Calcium. Let me know when he has eaten and we can go back into Wi-Fi.