Revelation 2:11

2:11 The one who has an ear had better hear what the Spirit says to the churches. The one who conquers will in no way be harmed by the second death.’

Revelation 8:8

8:8 Then the second angel blew his trumpet, and something like a great mountain of burning fire was thrown into the sea. A third of the sea became blood,

Revelation 20:14

20:14 Then Death and Hades were thrown into the lake of fire. This is the second death – the lake of fire.