Feedback and suggestions in comments is always welcome.

Intro

This build focuses primary on max range and secondary on as much damage as possible. Since [Saryn] is very efficient at defeating enemies and to help maintain that energy gain. It only needs [Equilibrium] that makes health orbs count as energy as well at full health. Spores are cheap to cast but Eximus can sometimes be uncommon spawning when needed. Of course, for this to work. You would need a companion that helps picks up health and energy as well as good at staying alive.

Roar works like a faction damage bonus that works on both Warframe weapons and abilities. Not only that. It works with Toxic Lash. Also Roar will increase Spores damage regardless if enemies were infected before or after when Roar is cast.

If it becomes difficult staying alive in battle. Protective Sling from Vazarin focus is the best safe guard. Also, Augur Reach helps by recharging shields when casting abilities.

Archon

100% Armour Remove & +45% Ability (Faction-like) Damage

• Tauforged Emerald (x3) for:
  • Gain +15% Ability Damage on enemies affected by Corrosion Status
• Emerald (x2) for
  • Increase max stacks of Corrosion Status by +2

You only need 4 stacks from archons to fully remove armour. By default, enemies can only have 10 stacks of Corrosion. Just adding Corrosion status adds 20%. Plus 6% for each stack. 104% = 20 + 14 x 6. One stack less will be 98% armour removal.

How-to Play

Pretty easy to play really. Either start with Spores or Toxic Lash to get health and energy from enemies. Then if Spore isn't active, start the spread and then activate Roar. Keep both Spore and Roar going and try to avoid the Spores decaying.

If you need to clear a room quickly. Use Miasma ability but be prepared to find replacement enemies to cast Spores on.

If you want to get as far as possible in Elite Sanctuary Onslaught. I would recommend bringing a friend/random using [Mirage] with [Explosive Legerdemain]. I've reached wave 18 with just myself, with this [Saryn] build, and a random with [Mirage].

Giving [Saryn] +100% Ability Range with Helminth Invigoration helps a lot too.

Last Notes

This build was capable of reaching 2nd place on the Elite [Sanctuary] Onslaught leaderboard near end of the week. Of course, with another player with [Saryn] and another with [Mirage].

If you need more power. You could switch [Augur Reach] with [Augur Secrets] and [Cunning Drift] with [Power Drift] but personally I wouldn't recommend it.