In contrast to a Defender, Eunectes functions more like a Duelist Guard (Dreadnought). She has a mountain of stats with her S3 up that very few units can match, enabling her to do some crazy things like take on a Patriot in a 1v1 match. Unfortunately, she also has a number of flaws that make her unviable, including high costs, low uptime, the inability to perform a skill-up 1-block, and an awkward trait that makes her unreliable in many ways. Although she views her S3 as her main source of income and considers its optimization to be crucial, due to her challenging usage, it is best to give it lower priority as a Mastery.
Her S2 is noteworthy because it is an absolutely absurd stun that nobody else can match. Although it has been used in high-risk situations in the past, it is currently best not to invest in Mastery outside of personal desire because it can be challenging to set up properly.