Sin is personified, and evil is personified, just as "the natural man", (which I already also mentioned), is personified. The passage you reference need not be plural, as you suggest, if it is speaking of the natural man or the nature of the natural man. The "old man" nature is singular, not plural, and speaks to the condition of all mankind before entering into the faith. Why singular? Because all mankind, before entering into the faith, sooner or later acquires "the spirit of the world" along life's way, (life outside Meshiah).
The spirit of the world is spoken of as one spirit, (1 Cor 2:10-12), but spoken of also in terms of many antichrists, who went out from among the faithful because they were "not of us". This is no doubt likewise the prince of the power of the air, spoken of by Paul in Eph 2:1-3, judging by the context surrounding that phrase, the same spirit of the world which is the spirit that now works in the sons of disobedience: among whom also we all had our conversation in times past, in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others.
The mark of his name in Rev 14:11 is no different than what is said in chapter thirteen: his name may indeed be speaking of the natural man personification which applies to all mankind. The natural mind of the natural man cannot please Elohim because it is enmity against Elohim, (Rom 8:5-8), and is therefore surely "antichrist".