"Sky Scourge", known as "Sky Demon God" in the OCG, are the weaker versions of the Chaos Monsters with "Invicil" having another effect similar to "Jinzo" or "Spell Canceller", depending on what Type and Attribute monster is Tributed.
Sky Scourge Enrise
"Enrise" is a more befitting representation of "Chaos Sorcerer", rather than "Black Luster Soldier - Envoy of the Beginning", since it is only capable of banishing face-up monsters, compared to "Black Luster Soldier - Envoy of the Beginning's" enhanced ability to banish both face-up and face-down monsters. It also cannot attack twice in any given turn.
This card places a heavier emphasis on LIGHT monsters to be banished than "Norleras".
Sky Scourge Norleras
"Norleras" is based on "Chaos Emperor Dragon - Envoy of the End", except you are now allowed to draw 1 card as part of the effect, after all the other cards have been sent to the Graveyard. In addition, there is no burn damage from the cards sent to the Graveyard. It is also more difficult to Summon than "Chaos Emperor Dragon - Envoy of the End".
This card places a heavier emphasis on DARK monsters to be banished than "Enrise".
Sky Scourge Invicil
"Invicil" is typically a weaker version of "Jinzo" for the most part, and is thus looked over in favor of it because of this. However "Invicil" negates Trap Effects anywhere, including the Graveyard, which can sometimes be more helpful for cards like "Breakthrough Skill" and True King/Draco Trap's Graveyard Effects. "Invicil" would clearly be a stronger version of "Spell Canceller", except Spell Canceller will have it's effect regardless of what monster you use for it's Tribute Summon.
Ritual Sky Scourge
With the use of "Advanced Ritual Art" with Ritual Monsters such as "Demise, King of Armageddon" or "Ruin, Queen of Oblivion". You can effectively send 4 level 2 Normal DARK Fiend or LIGHT Fairy monsters. While the TCG may only have a handful of each of the Type legal. "Wretched Ghost of the Attic", "Souls of the Forgotten", and "Meda Bat" for Fiends. With only "Happy Lover" and "Mystical Shine Ball" for Fairies. However your options are increased if you decide to use level 1's and a few level 3's with this, however you will most likely find this even less consistent than it was previously because of all the non-tuner different level Normal Monsters. Having your monsters level 2 will have the cleanest number in your Ritual Summon while sending exactly 3 LIGHT Fairy monsters and 1 DARK Fiend monster or Vise Versa for the Ritual Summon. You will also have access to cards like "Manju of the Ten Thousand Hands", "The Agent of Creation - Venus", and "Unexpected Dai" as it can Summon any Tribute fodder you need for "Sky Scourge Invicil". After using your Ritual Monster's effect or just attacking for massive amounts of damage with Norleras or Enrise, you can make a powerful Rank 8 Xyz Monster after destroying the field with Demise or attacking for major damage with Ruin.
Sky Scourge as a pure deck is nearly impossible to construct, as there are almost no LIGHT Fairy monsters that work well with DARK Fiend monsters. This will lead to the conclusion of playing monsters that are powerful but have no synergy with each other. Making your deck have almost no way to gain card advantage and will have a very slow time of getting cards to your Graveyard that you need to summon your Sky Scourge monsters.
As any Graveyard dependent deck that needs monster effects, this deck has major issues with stun decks with cards like "Macro Cosmos" and "Skill Drain". This will prove even more difficult to deal with than normal because you will need to play massive amounts of monsters in order to play your Sky Scourge Monsters. Which will leave only a small amount of room to deal with problem cards that hinder your monsters or your Graveyard.
"Sky Scourge Enrise" itself is just a weaker version of "Black Luster Soldier - Envoy of the Beginning" and a much more difficult to summon and less searchable "Chaos Sorcerer". Meaning the only reason you would play this card is for it's Type, Attribute and Level (Or just because you can or want to). When this card was released originally, Chaos Sorcerer and Black Luster Soldier - Envoy of the Beginning were banned, but currently they are not, and they are much better in almost all scenarios.
"Sky Scourge Norleras" is the only one of the 3 Sky Scourge monsters to ever see successful play in large Yu-Gi-Oh events, as it has the most powerful effect. Decks such as "Hopeless Dragon", and a handful of Dark Armed Dragon decks would play Norleras only has a discard material for cost or just send it to the Graveyard with the effects of "Foolish Burial", "Dark Grepher", and "Armageddon Knight". Then use the effect of "Phantom of Chaos" to copy the effect of Norleras, effectively turning the game into a top deck war in which the Norleras player had a head start.
However many years later, other players started using this card again, but instead of using Phantom of Chaos primarily, they used Norleras' true summoning conditions, in "Burning Abyss" and "Fluffals" during 2016. While considered gimmicky in Burning Abyss because it needs to banish a "Beatrice, Lady of the Eternal" or a "Dante, Pilgrim of the Burning Abyss" in order to summon. In many cases, the card proved insanely powerful on use, as the vast majority of Burning Abyss monsters have effects that activate when they are sent to the Graveyard as well as drawing a card proved very powerful. Also because Norleras is removal without destruction, they did not have to worry about cards like Beatrice or "Kozmo Dark Destroyer" being activated by Norleras' effect. While not being a card that everyone played in Burning Abyss, it was definitely a card many players considered and sometimes respected as a powerful deck choice.
- Each "Sky Scourge", being Super Rare, has minimal Holographic foil. This is evident on "Norleras", who only has foil on his talons and spikes.
- The poses of "Norleras" and "Invicil" suggest that they are flanking "Enrise" ("Invicil" is looking right, our left, and "Norleras" is looking left, our right).
- The Sky Scourges seem to be on a battlefield of some sort; "Enrise" seems to be wearing part of a military uniform, and all three have barbed wire in the background.