A miracle, in general, is a manifestation of supernatural power that has an effect and purpose in the physical universe. Evil miracles, initiated by the devil or his demons, are performed with the purpose of turning humanity away from God (Matthew 24:24, Revelation 19:20) or to simply bring pain, suffering and trials to humans.
Rebellious spirits carry out evil miraculous acts, either directly or through those they use, utilizing the spiritual power they possessed before they became enemies of God. The Lord sometimes allows them to exercise their abilities in the world so that those who reject him may be further deceived (2Thessalonians 2:9 - 12) or to test those who obey him.
Examples
The book of Job records some of the earliest wonders carried out through the agency of evil. The devil first brought fire from heaven in order to kill all of Job's sheep and murder his servants (Job 1:16). Satan then used his authority over earth's weather to bring an unusually strong wind upon a house that resulted in the death of all of Job's adult children (verses 18 - 19).
Evil beings can even mimic some of the same physical manifestations as God. Pharaoh's magicians were able to duplicate Moses and Aaron's power of turning a rod into a serpent, converting fresh water into blood and bringing a frog swarm upon Egypt (Exodus 7:10 - 12, 22, 8:6 - 7). They were unable, however, to replicate the last eight of the ten plagues that fell on Egypt (Exodus 8:18).
One day Jesus encountered a man who had thousands of demons (a "legion") in him (Mark 5:9). They gave the man the super-human ability to constantly live outside while completely naked (Mark 5:3, 5, Luke 8:27, 29). They also enabled him to break any chain, fetter or restraint used on him (Mark 5:3 - 4).
Soon after the New Testament church was born, a man influenced by evil named Simon Magus was able to work awesome wonders that amazed the people of Samaria. His demonically inspired black magic was so spectacular and convincing that people we awed and listened to what he taught (Acts 8:9 - 11).
The greatest evil
The Bible warns that, in the End Time, the forces of evil will show an unparalleled number of signs and wonders. Jesus himself warned that false Christs and false prophets would show great miracles with the goal to deceive people.
For there shall arise false Christs, and false prophets, and shall shew great signs (Strong's Concordance #G4592) and wonders (#G5059); insomuch that, if it were possible, they shall deceive the very elect (Matthew 24:24, KJV).
The greatest display of the power of evil miracles, however, will be reserved for the Beast and the False Prophet.
And he (the False Prophet) doeth great wonders (#G4592), so that he maketh fire come down from heaven on the earth in the sight of men, and deceiveth them that dwell on the earth by the means of those miracles (#G4592) which he had power to do in the sight of the beast . . . (Revelation 13:13 - 14, KJV).
The same Greek word translated as "signs" in Matthew 24:24 is the same one used to derive, in the King James, the words "wonders" and "miracles" in the above verses.
The end time False Prophet will display such miraculous powers that he will be able to convince the world not only to adopt the Mark of the Beast but also to worship him as if he were god on earth (2Thessalonians 2:4, 2Corinthians 11:13 - 14)! Jesus' return, however, will cut short their rule and cause them to receive the penalty they deserve for their evil.
And the beast was taken, and with him the false prophet that wrought (evil) miracles before him, with which he deceived them that had received the mark of the beast . . . These both were cast alive into a lake of fire burning with brimstone (Revelation 19:20, KJV).