Experimental Null Star Bomber build here. Gimme feedback! :)

This is an all-purpose Slow/Fast [Nova] build.

GUIDE REWORKED!
[Nova] has been given a rework with Warframe Update 37 (patch notes).
Biggest change: There's no need for a separate low strength Speedva build anymore!

The build is designed to slow down or speed up all enemies around you with your fourth ability (Molecular Prime) by up to 75% while also increasing the damage they take from all sources. I tried to use plenty of easily accessible mods since chances are high you might not have everything in the game yet.

This is how it works:

• Molecular Prime sends out a wave, slowly travelling outwards and coating all enemies it hits with antimatter. Depending on your ability strength, these units will be slowed down or sped up (see Fast Nova). Coated foes will also take double damage and might explode on death.
• Tap the ability button to slow enemies, hold it to speed them up.
• Ability range does not affect the wave. You can't change the wave's travel speed, so in order to increase its effective range, you need to pump up ability duration (to keep it active and moving for a longer time).
• You can achieve the maximum amount of 75% slow/speed by modding 150% ability strength.

• The [Molecular Fission] mod will consistently recharge your Null Star (first ability) particles. This greatly improves your tankiness and survivability, since every active particle reduces incoming damage by an additional 5% - resulting in a permanent 90% damage reduction with 18 or more particles active. The reduced range of this build further helps you keeping up this damage mitigation since the particles will only fly off seeking nearby targets when enemies are in very close proximity to you.

• Not tanky enough or lacking energy? Replace Streamline and/or Augur Message with Equilibrium (which works well with Nova's new passive), Adaptation or Rolling Guard.

• Regular Continuity is perfectly fine if you do not have the Primed version yet. :)

Some more in-depth mechanics:

• Null Star with Molecular Fission uses the priming setting (slow/fast) of your most recent Molecular Prime cast.
• Vulnerability: The description says "200%". In this case, it is a 2x damage multiplier, NOT plus 200% on top. If you compare this to Atlas' Petrify ("50%" which results in a 1.5x multiplier), these descriptions are inconsistent.
• Speaking of Petrify: These vulnerabilities stack multiplicatively, not additively. So a primed and petrified enemy being shot at with 100 damage results in 10021.5=300 damage. (If the vulnerabilities would just add up, you'd get 100*2.5=250 damage.)

Aura:
This build doesn't require a specific Aura mod. Use whatever you have and/or prefer.

• I added an Aura Forma (not a regular Forma: Wiki article), since it enables me to use differently polarized auras for various builds. If you don't have one or do not care about other builds, feel free to skip it.
• Suggestions: Corrosive Projection, Dreamer's Bond, Growing Power, Power Donation
• Same polarity as Neutral and Fast builds: Growing Power, Steel Charge or Rifle/Pistol/[Shotgun Amp]

Polarities and Forma:
You don't necessarily have to set up the polarities exactly like I did here. Since I'm tinkering with different builds alot, this setup has proven to be quite nice for my preferences.

Arcanes:

• Since I'm using this build solely for high level missions, I prefer to tank up as much as possible. Grace and Guardian are my standard choices for this.
• Energy usually isn't that much of an issue since you don't need to spam abilities, so Energize isn't necessary.
• Feel free to use whatever Arcanes you prefer/own.

Subsume:
There are tons of useful options here. Dispensary, Roar, Breach Surge, Thermal Sunder, Empower...whatever fits your playstyle.

Shards:
I'm using 2xCrimson for Ability duration as well as 3xAmber for Cast Speed, Parkour velocity and More energy on spawn. THis is mostly for quality of life, so don't worry or adjust it to your preferences. Ability strength is another good option, since the rework made modding for low/negative strength obsolete.

TIP: If you don't want to slow down defense missions you still can bring a lower strength [Nova]. You're still providing the damage bonus and explosions while avoiding that one guy raging about everything taking too long. This can also prevent your squad from being overwhelmed by fully sped up enemy waves while still helping to run a Defense mission faster. Or you can run a flex build at ~100% modded strength and subsume Empower (+50% strength for one cast) to max out the speed/slow effect by the push of one extra button.

Alternative lategame/expensive build:
This is what I'm currently using. Precision Intensify allows me to run Power Dono while still maxing out the slow/speed. Nira is a placeholder until I've figured out what I wanna do with that slot and maybe a subsumed ability...

There's always some more potential to further minmax, but I like this build and its moderate amount of polarized slots, leaving room for variations and alternative configs.

Questions? Feel free to message me ingame or via Discord. :)
Warframe tips and beginner's guide here.