If you thought the developers of the game had decided to finally give up on this archetype, you were wrong: the new Main BOX, Stardust Acceleration, features more Gemini support.
This deck focuses on Special Summoning Black Brutdrago, a Level 8 Synchro Monster with 3000 ATK and the ability to destroy the opponent’s backrow, using Tuned Magician and a Level 4 non-Tuner Gemini as mater
Dark Valkyria has the ability to destroy a monster on the field, she is arguably one of the best Gemini Monsters because of this effect. Black Brutdrago can deal with the opponent’s backrow while Dark Valkyria can get rid of problematic monsters like Wiz, Sage Fur Hire that could limit you.
With Synchro Summoning being added to the game and Yubel Fire King becoming so popular, Heavy Knight has gotten even better; this monster has the ability to banish before the Damage Step a monster that was Special Summoned by attacking it.
You don’t need a Gemini Tuner in order to Special Summon Black Brutdrago, but there aren’t any other Level 4 Tuners and Tuned Magician still has synergy with Gemini Spark.
You need to Gemini Summon Tuned Magician in order to use it as a Tuner—the easiest way would be to use Supervise or Unleash Your Power!, the Quick-Play Spell from Stardust Acceleration.
This Quick-Play Spell is the best support that the Gemini archetype has ever received—it can destroy any card on the field and it lets you draw a card right afterwards by tributing a Level 4 Gemini Monster. Since Gemini Spark is Quick-Play Spell, you can force your opponent to activate their backrow by attacking with one of your monsters and then chain it to the activation, unless it was a Damage Step card like Mirror Wall, which is quite uncommon right now.
Gemini Spark makes it easier to draw into the cards you need to summon Black Brutdrago, it can be used to prevent Fur Hires from swarming the field or to get rid of an Amazoness Onslaught before it’s able to banish one of your monsters.
Thanks to Balance, you are guaranteed to start with at least one Spell Card in your hand, which is going to be Supervise 50% of the times. This Equip Spell allows you to activate the effects of your Gemini Monsters without having to Normal Summon them a second time, giving you access to Dark Valkyria and Heavy Knight of the Flame's removal effect and making Tuned Magician a Tuner.
If Supervise is sent to the Graveyard, you can Special Summon a Gemini Monster from the Graveyard—this effect is great if you are going first because the opponent will have more trouble OTKing you.
This Trap Card is one of the best in the game right now, it slows down a lot of the current top-tier decks like Fur Hire and it can also be Special Summoned after it has been sent to the Graveyard by chaining it to a Trap Card on the field.
Canadia can’t unfortunately be used as material for Black Brutdrago, but, if you manage to get two on the field together with a Tuned Magician that has gained its effect, you can use it to Synchro Summon Stardust Dragon.
There is only one copy of this in the deck, but you have a higher chance to start with it thanks to Balance than to draw into it after you have already used a Trap Card; since Canadia is banished when it’s sent to the Graveyard after it has been Special Summon as a Level 2 WATER Aqua monster and Birthright is a Continuous Trap, Treacherous doesn’t automatically turn into a dead card all of the times if it wasn’t in your starting hand anyway.
Keeping your monsters on the field is not always going to be possible, but you need to have at least two in order to Special Summon Black Brutdrago; Birthright can Special Summon a Normal Monster from the Graveyard with its effect.
Since Gemini Monsters are considered Normal Monsters while in the Graveyard, you can target them with this Trap Card; you can tribute one of your monsters with Gemini Spark and then Special Summon it with Birthright.
Birthright has more synergy with the deck compared to Powerful Rebirth because the latter would increase the Level of the monster revived by 1, but you can substitute it with Soul Resurrection, if you don’t have it.
Stardust Dragon is the secondary Boss Monster of the deck—there aren’t that Synchro monsters yet, so we are quite limited in terms of options.
Stardust Dragon can negate cards effects that would destroy something on the field (Treacherous Trap Hole, Vampire Kingdom, Donpa, Marksman Fur Hire, Recon, Scout Fur Hire, etc.) by tributing itself and then come back from the Graveyard during the End Phase.
By discarding a Gemini Monster, once per turn, Black Brutdrago can destroy a Spell/Trap Card on the opponent’s side of the field—even though this effect is kind of slow against decks like Amazoness that rely so heavily on their backrow, having it is still great because it means that there is less of a need for cards like Hey, Trunade! or Cosmic Cyclone that would essentially make the deck less consistent.
When Black Brutdrago is destroyed—either by card effect or by battle, if there’s something that can get over this 3000 ATK monster—you can Special Summon a Gemini Monster from your Graveyard and give it its effect right away. The main threat for this card are Amazons and their Continuous Trap: Amazoness Swords Woman can cause 1500 damage to you by attacking into it and, if Amazoness Onslaught is on the field, Brutdrago is also banished, which means you are not going to get his secondary effect off.
Balance is used to guarantee at least one Monster, one Spell and one Trap Card in your starting hand; you are guaranteed to start with Gemini Spark or Supervise, both of which give you more survivability.
Wiz, Sage Fur Hire is a constant threat as it can negate Gemini Spark and Supervise, but its effect is limited to a “once per turn” use, which means that you could still force its activation with a Canadia and then activate whatever you want freely.
Dyna, Hero Fur Hire, the biggest monster in the deck has trouble getting over Black Brutdrago without at least another Level 5 or higher monster on the field and Donpa, the other way of getting rid of it is now limited to two copies. Fur Hires might be too fast for this deck—setting up takes a long time and you don’t have this kind of luxury when you are facing them.
If your Gemini Monsters are banished, you can’t Special Summon them from the Graveyard with Supervise, Birthright or with Black Brutdrago’s effect;
Amazoness monsters can just attack into your own monsters with little to no drawback.
Your backrow and Dark Valkyria are going to play a big role in this matchup: your objective is to stall until you can summon Black Brutdrago and get rid of the Continuous Trap.
Vampire have a “once per turn” removal in Vampire Kingdom and they don’t mind having their monsters destroyed by Dark Valkyria or Gemini Spark since Samurai Skull and Gozuki can just float into another monster.
Vampire Vamp can just target Black Brutdrago or Stardust, the two monsters that you have put so much effort into summoning, with her effect to get rid of them and gain their ATK; Vampires are generally too strong and consistent for this deck. Your best bet is to use Canadia to stall and then get rid of Vampire Kingdom with Black Brutdrago—after setting up, Vampire players usually find themselves at around 2500 Life Points and most decks don't feature much backrow at all for protection.
Masked HEROes focus on ending games quickly using Mask Change, their Quick-Play Spell, multiple times in a turn; going first against this deck is pretty rough as a Hey, Trunade! or a Cosmic Cyclone, both extremely common cards, could get rid of your backrow and leave you with no protection.
On the positive side a Masked HERO Anki would have trouble getting over Black Brutdrago, but the backrow removal effect wouldn't be of much help since most Masked HERO decks don't actually run that many Spell/Trap Cards for protection aside from Treacherous Trap Hole.
Paleozoic Canadia and Gemini Spark can respectively flip face-down and destroy U.A. Midfielder before the opponent is able to switch it for one of the higher Level U.A. monsters, but Cosmic Cyclone could prevent this; U.A. Penalty Box can be an issue, but Black Brutdrago can still get rid of it with its effect.
Spellbooks can deal pretty well with this deck: Spellbook of Fate can banish your monsters, preventing you from Synchro Summoning, and Silent Magician can negate Gemini Spark and Supervise with its effect.
The advice is to get rid of the Spellcaster on the opponent's side of the field with Spark or to flip it with Canadia before they are able to set up the Graveyard. If you suspect the opponent is playing Spellbook and you are going first, turn the Toggle Button ON so you can chain Gemini Spark to a Spellbook Magician of Prophecy being set and prevent Silent Magician from being summoned.