The Evil Spirit Incarnate, known more commonly by fans as "Scyther" or alternatively the "Reaper", is the primary antagonist in Metal Slug 5. Though its origins and purpose are unknown (the game makes no mention of its existence until the final battle), it is the true mastermind of the game's events, having been manipulating the Ptolemaic Army through the white masks used by their cult leaders.
One thing is certain: it's susceptible to conventional human weaponry, enough to send it packing after prolonged damage. So despite its fearsome appearance and notable power, it's not all-powerful by any means.
Its weak spot is the skull on its chest. The gigantic demon will cast energy spheres that track down the player. After a short time, it will cast a large amount of spheres and fly away. The demon's shadow will appear in the background, raising its scythe to attack where the player is, thereby indicating a planned attack spot, and giving the player a moments notice to get out of its way. Merely dodging the scythe is not enough, as the scythe will create a spray of deadly arcing smoke projectiles upon impact with the ground. Once damaged enough, several explosions will appear on the demon and it will fly away, possibly having been mortally wounded, preventing us from ever knowing exactly what this behemoth was.
- To date, the Evil Spirit Incarnate has the largest sprite size in the series.
- The Evil Spirit Incarnate resembles the alternate flag of the Rebel Army. It also bears a passing resemblance to The Grim Reaper - given the occult nature of the Ptolemaic Army's doings, some fans believe the Evil Spirit Incarnate to be Death itself, given form and summoned to do the Ptolemaic's bidding. Others think it is a demon of some kind, or possibly even the Devil. It could also simply be an extraterrestrial life form, given the starry night appearance of its "skin".
- At the beginning of the fight, the players' characters use their cold/chill animation, suggesting that the boss may have a cold body or the atmosphere that the fight takes place in is very high where a person may get cold.
- A common name that the fans use for the Evil Spirit Incarnate is Scyther. However, Scyther is also the name of a Pokemon, debuting in Pokemon Red and Pokemon Blue, before Metal Slug 5.
- Fans speculate that the Native who had found the mask, and was struck by lightning, is the large demon. The Native may had morphed into a demon, with the reasons maybe due to the struck lightning, or because of the "ancient" stones which are in the game's unused files, along with the leader's tower. This theory has now been proven to be false due to the existance of Ptolemaios in Metal Slug Attack.