Coming down out of heaven (katabainonta ek tou ouranou). As in Rev 10:1; Rev 18:1.
The key of the abyss (tēn klein tēs abussou). As in Rev 9:1.
A great chain (halusin megalēn). Paul wore a halusis (alpha privative and luō, to loose) in Rome (2Ti 1:16, as did Peter in prison in Jerusalem (Act 12:6).
In his hand (epi tēn cheira autou). “Upon his hand,” ready for use. See epi with the genitive in Rev 1:20.