Prismata isn't a game where memorizing openings is generally that useful, since the set is different every game and half the time there are alternate Drones that throw all this to the wind; but I'm not going to jump on the "never memorize anything" bandwagon that a lot of top players did back in my day. I think it's obvious that talking about the most common openings and when they're good can be useful.
I've tried to sort them in order of increasing economy, not decreasing usefulness. Also, some time after I posted this 307th put up the Prismata Library which contains this post. It only covers the most common openings whereas mine tries to list everything that might ever be good without involving non-standard Drones, but his goes into more detail about the most useful openings and contains nice fancy screenshots. On the other hand, the names he gives to the openings are a lot less fun than the ones I give :)
- A - Crazimus
This is quite a crazy opening indeed. There may not be any sets where this is winning (though I've lost to it multiple times). Only use when you're sure anything else would lose to p2 Crazimus. In particular, look for Immolite, Perforator, Ferritin Sac, etc.
- DD/DC - Fastuit
This is p1's only viable line in Zemora Voidbringer games or Tia Thurnax rush sets where it's just that important to get green early, but outside of that you're usually better off with Slow Conduit or Double Conduit.
- DD/DB - Fastforge
A rarely useful opening. It's often the best counterplay to Crazimus from p2 (or some similar rush), and can also be good with Flame Animus or sometimes Synthesizer.
- DD/A - Elyot Animus
Very bad opening most of the time, but sometimes you just have to get the first Animus (Electrovore/Grimbotch sets where p2 Fastimus would beat anything else). The problem is that you end up eternally floating 2 gold if you just spam double Tarsier (or other 4R attacker) after this. You can go TDD after it to mitigate this issue, but then you're wasting a red and it was probably better to just go Natural Animus. This opening is made a lot better by the presence of Immolite or Perforator (because you can go T1D after it) as well as Vivid Drone, Doomed Drone or Galvani Drone (because you can spend the extra 2 gold on economy).
- DD/DD/DDA - Natural Animus
The standard p1 red line. I'd say this should be thought of as the default in any set where you don't want a third Engineer and the best attacker is red. It's also p1's best Feral Warden line because it can easily be followed with TTC.
- DD/DD/DDB - Natural Blastforge
Mostly used when there's a blue economic unit, like Flame Animus, Ebb Turbine, Synthesizer, etc. It's also a good response to whatever rush p2 might be playing if you don't think mirroring can win, as you can immediately Wall against p2's first attackers.
- DD/DD/DDC - Slow Conduit
This opening is kinda painful because you store 2 gold twice in a row, but sometimes it's just the best timing.
- DD/DD/DCC - Double Conduit
A possible setup for Tantalum Ray or Gauss Fabricator rush.
- DD/DC/DDC - Double Fastuit
The follow-up to Fastuit if you want to get Zemora Voidbringer. It's also an alternative to Double Conduit if you want fast Tantalum Rays. Finally, it's my go-to line when I play Venge all-ins as p1, but I'm terrible at Venge games...
- DD/DD/DCB - Fast Blastuit
This is a pretty niche opening. You can use this to rush Borehole Patrollers (and I did that gleefully when I was a newb) but you generally shouldn't unless there's Lancetooth or something in the set. It could also be a Flame Animus setup if you would otherwise go Natural Blastforge but want an early Conduit too.
- DD/DD/DDC/DDB - Slow Blastuit
Extremely painful due to all the floating, but sometimes, if this is the tech progression you want, it can be worth it. One example that comes to mind is you're being red rushed and want to get to Plasmafier to counter it.
- DD/DD/BA - Aniforge
This one leaves you overteched in base set, but with Hellhound + some red support like Immolite or Perforator or something it can be good.
- DD/DC/DA - Fast Condimus
Pretty bad opening because you're cutting a huge amount of econ, but somtimes you've just got to be the first one to the Endotherm Kit or something. You should not usually use this to set up for Scorchillas unless there are alternate Drones in the set that smooth out the build such as Vivid Drone.
- DD/DD/DDC/DDA - Slow Condimus
A slower red green setup. Decent Scorchilla opening, also can get you to Cynestra or something.
- DD/DDE/DDD/DDDB - Econ Blastforge
Standard p1 line for high-econ sets with a big blue unit like Odin or Omega Splitter, or a good blue unit to open with (again Flame Animus, Synthesizer, and Ebb Turbine come to mind). The Blastforge just fits so well into the build.
- DD/DDE/DDD/DDDC - Econ Conduit
A bit less natural than Econ Blastforge, but sometimes early green seems important, like if there's Xaetron or something, or you just don't have anything you'd like to buy with the blue this early.
- DD/DDE/DDD/DDDC/DDDA - Econ Condimus
Reasonably natural, and gets an Animus in a timely fashion. This is my go-to build in high-econ Cynestra sets, for example, or just high-econ sets where the best attacker is Tarsier - you'd like to get an Animus first, but you can't, so you go Conduit instead because it's not a big commitment.
- DD/DDE/DDD/DDDE/DDDDA - Super Econ Animus
Warning: fourth Engi builds are extremely niche and should only be busted out in sets with both a massive absorber and really good soak and preferably no efficient attackers either. When you do want them, Animus is probably the best tech building to start with because if there's an efficient random set attacker you probably should've gone for it faster, which means if it was correct to play 4th Engi then Tarsiers are probably the best attacker.
This can sometimes be correct in Zemora Voidbringer sets, or maybe Scorchilla sets if there's Vivid Drone or something so you don't have to float 2 gold next turn. In general, though, Natural Conduit is better.
Same as p1 Crazimus. Since p2 Fastimus is already very strong in most red rush sets, the only reason to do this is if early red looks so strong that you're scared of Elyot Animus. Make no mistake, I think it takes a minimum of 3 units to make this opening win against BSO (Vore + Immo + Nitro should do it I think).
The typical setup for p2 red rushes. You likely want this in games with Blood Phage, Electrovore, Bloodrager, Amporilla, etc.
This opening is unnatural, so it's mostly used as a response to Elyot Animus or something (since it allows an immediate Wall), or for a blue unit that's good to open with like Flame Animus or Synthesizer.
Probably the best and most common opening in the game overall. This opening is excellent in almost any set where early green is good.
Pretty rare, but I imagine it's good in Feral Warden rush games with red support like Grimbotch or Electrovore.
Standard setup for double Scorchilla, Tia Thurnax, Cynestra, Endotherm Kit... you name it.
This opening is also pretty niche, because it commits to a lot of tech on a low economy but still doesn't count the Blastforge you probably need, so you're usually going to be overteched once the opponent counterattacks. However, if there is a green sink unit in the set like Cluster Bolt or Trinity Drone, the green commitment will be lessened, making it a good way to rush Endotherm Kit or maybe Cynestra. You can also use it for Tia Thurnax, but be warned that it's too fast to even win versus BSO unless the opponent is playing right into it (an early Animus, no Blastforge yet).
The go-to opening in Zemora Voidbringer games. Also good with Tantalum Ray or other green units maybe.
Standard opening for any sort of midrange blue-green set. Usually followed with a unit like Urban Sentry, Borehole Patroller or Tesla Coil, etc.
The standard setup for Tatsu Nullifier or Shadowfang rushes. Shadowfang rushes are just bad though (barring some very specific contrived sets like Fang+Perforator+Ferritin Sac or something), and Nullifier rushes, while not completely useless, do also lose to BSO if the opponent plays a mono-red response. You may want to go for a Nullifier rush if the opponent drops a Blastforge and there is some significant support for you (eg. Perforator), but outside of that, this opening is almost universally bad.
I believe this is p2's best line in base + Hellhound.
The usual setup for Deadeye Operative (although toward the end of my day some pros were starting to talk about 3rd Engi in Deadeye games; I never tried that out much). Can also be used to rush Drakes or Grenade Mechs as a counter to p1 going for a strategy vulnerable to pressure.
This is p2's equivalent of p1's Slow Conduit, but it's even worse. Nevertheless, even this painful build is optimal in some cases. For example, I think it's as close as p2 gets to winning base + Infusion Grid or base + Doomed Wall.
Often feels forced in high-econ sets because the alternative is to float 4 gold 2 turns in a row (or 3 the next turn if you get Animus instead of Blastforge). Nevertheless, it's quite good most of the time, so there's rarely a reason to be dissatisfied.
The usual follow-up to Econ Conduit, as it spends all your gold perfectly and gives a color you almost certainly want at some point anyway. The Blastforge will allow you to get a Wall if p1 is rushing you, or a Steelsplitter to make them get a Wall.
Note that this cuts a Drone on turn 4. It's painful, but it can be worth it if you can get TTDDD or something next turn. I believe this opening wins base + Mahar Rectifier.
An alternative to Econ Blastuit if you want heavy green sooner, such as Xaetron or Mahar Rectifier.
Similar notes to the p1 Super Econ Animus above. 4th Engi is niche. When you do want it, this is usually a good choice of tech progression because odds are there is a green soak unit and no attacker better than Tarsier to make it 4th Engi.