Taking the mark of the beast, as described in Revelation 14, leads to severe consequences, including drinking the wine of God's wrath and being tormented forever. This mark signifies worship of the beast and its image, which is strongly warned against in the scripture.

Revelation 14:9-11
King James Version
9 And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand,

10 The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb:

11 And the smoke of their torment ascendeth up for ever and ever: and they have no rest day nor night, who worship the beast and his image, and whosoever receiveth the mark of his name.