Overview
Nidus is an Infested based Warframe. Unlike most frames, he does not have any shields and cannot receive overshields; all damage he takes will hit his health directly. He also cannot benefit from shield gating.
He compensates for this lack of shields with inherent health regeneration. Armor is also much more effective on him since all incoming damage will be mitigated by it.
Directory
Relevance
Nidus is a great general use Warframe. He has great CC, group healing, and a great buff or damage mitigation. His lack of shields increases the effectiveness of Armor. This makes him a perfect candidate for Umbral builds and Umbral Forma.
Nidus will likely never be the best at any one job, but if I had to pick only one Warframe to play forever, it would be Nidus.