Took out Fan of Knives and Sap, because they weren't doing enough versus aggro, in particular Healzoo and Spell Hunter. Put in a second Elven Minstrel to compensate for the card draw, Cavern Shinyfinder to be able to more consistently find the weapon and to have something more to play on turn 2, Rotten Applebaum to buy some time and finally Wargear to make the mech package more worthwhile.
Inspired by Chump's Star Aligner Druid and Warlock decks, I decided to try and make a Star Aligner Rogue deck. With the new Necrium cards from Boomsday, I took a deathrattle approach.
I expected this to be a meme deck, but I played it from rank 19 to 15 in about 15 matches, so it might have more potential than pure meming. Later I first dropped from rank 13 to 14, but then climbed back up to 11. However, performance depends a lot on the meta: in a slow meta it works great, against fast decks you have to struggle to survive until you can strike back.
It does well against control and combo decks, since you can summon huge boards and have big damage spikes: getting a Warrior or Druid from 60 to 0 is not a problem, sometimes you can even do it in two turns. It is unfavored but not hopeless against aggro: I managed to get wins against Healzoo, Burn Mage and Odd Paladin.
Although Star Aligner is the eye catcher, the real star of the deck is Carnivorous Cube. Combined with minions like Mechanical Whelp and Charged Devilsaur plus the deathrattle triggers Necrium Blade and Necrium Vial, it can create huge boards. Once you have a good board, Star Aligner can be a way to break through a taunt wall or deal 7 extra face damage to finish off the opponent.
Versus aggro, for the first few turns just try to stay alive. You might have to use one of your Necrium cards on Blightnozzle Crawler to keep the board under control. Drawing Zilliax helps a lot: if you can land that on a high health or high attack mech, the healing will give you the time you need to develop a superior board. There is limited healing and removal in the deck, so you are still on a clock: trade into the most dangerous minions and apply counter-pressure on your opponent's face with the rest.
Versus control, spend the first turns drawing extra cards with Elven Minstrel or Cavern Shinyfinder, discounting your mechs with Galvanizer and setting up a Necrium Blade. You can try to set up for Star Aligner on turn 7 or 8, using Mechanical Dragon cloned by Cube and/or a 7-health minion summoned from Silver Vanguard. The stars rarely align on the first try though, because control decks have lots of ways to sabotage your plans, so don't go all-in on this.
I generally Cube Mechanical Dragon versus aggro and Mechanical Whelp versus control, but there is no hard rule: it depends on whether you need power on board now or you can afford to wait for a big swing turn with Star Aligner.
If you have no other good plays, you can just play Star Aligner as a 7/7, especially if you have a Cube in hand.
The Charged Devilsaurs are are only 8-mana minions in the deck, so Silver Vanguard will always draw one of those. You can use Lab Recruiter to shuffle more Devilsaurs into your deck, so Silver Vanguard stays useful.
In any matchup, the mechs are good keeps, even Mechanical Dragonling if you're on the coin or already found a Galvanizer. Necrium Blade and Cavern Shinyfinder are also a good keep: versus aggro you need the Blade to maintain board control, while versus control you can set it up to trigger a Cube on turn 6 or 7.
Keep Eviscerate versus aggro and mid-range.
Keep Elven Minstrel versus control. Versus aggro, only consider keeping it if you're on the coin, but even then you'd still rather have a mech or Blade to play on turn 3.
While Carnivorous Cube is the strongest card in the deck, keeping it in your opening hand risks having no early game at all. Maybe keep it if you already found Blade/Shineyfinder and Crawler/Whelp.
Star Aligner itself counts as one of the three 7-health minions you need, so you need only two on board, but more than two is also fine. Pay attention to the yellow glow in your hand.
When played from hand, Charged Devilsaur has an ability that is essentially rush. However, when summoned from Cube or Vanguard, the battlecry doesn't go off and it can go face immediately.
Magnetized mechs count as minions with enchantments on them. If you Cube them, only the base mech comes back out.
You can use Necrium Blade's deathrattle on the turn you play it by replacing the weapon using your hero power.
If you don't have Zilliax, I suggest a second Rotten Applebaum. Or if you have the dust, just craft it: in my opinion it's the Boomsday equivalent of The Lich King: a neutral legendary that fits into lots of decks.
If you have no Charged Devilsaurs, then it's not worth running Silver Vanguard. If you have one Devilsaur, you could put in another 8-cost minion. You could consider is The Lich King, but then you're not guaranteed to always recruit a 7-health minion. Another option would be Violet Wurm, but I'm worried a board full of Grubs would reduce the yield from Cubes, block you from playing more minions or play into Spreading Plague. Cauldron Elemental has the right stats and cost, but there are no other elementals in the deck, although with Cube you could probably make a board of Cauldron Elementals buffing each other. I thought about Grand Archivist, but that's bad with Preparation and I think that card is too valuable to cut.
You absolutely need two Carnivorous Cubes. But if you have any interest in deathrattle decks, you probably have already crafted those.