Hi all.
This build is born because i always loved [Hydroid] , but unluckly his abilities are mediocre at best and hardly he would be able to make the difference in a team willing to face an endgame challenge. The bright side of having meh abilities is that those don't need specialization, so you can avoid forma hungry extreme builds with corrupted mods and put survivability/utility mods instead.
Mod choice:

• [Pilfering Swarm] IMO is a must have in any [Hydroid] build, so putting a Zenurik polarity is a solid choice. If i wouldn't care about the extra loot, my choice would be Curative Undertow (still Zenurik)
• Umbral mods and [Adaptation]: Armor and Health will let you survive in medium level (till sortie level) missions. You can put a level 1 [Umbral Intensify] if you want to avoid to use a forma or you want to use a primed continuity, but i like to be able to kill low level enemies with the tentacles, so strenght is needed.
• Continuity: you will travel farest with Tidal Surge (good panic button)
• [Stretch]: Tentacles will spawn in a larger area. More range would be counterproductive because you have no way to increase the number of Tentacles (sigh)
• Streamline and Energy Siphon: Tentacles spawns sometimes in a non-sense pattern, so you have to spam your 4 more times for hit something, and have energy will help.

[Natural Talent] is a valid choice in place of [Stretch] or [Streamline], and will help you to charge your 4 faster