Obviously, the recommended weapons are the Laetum/Felarx/Phenmor with the Devouring Attrition incarnon perk (50% chance of 2000% damage on a non-crit) for dealing with the Necramechs. Melee doesn’t matter as much. Of course, these weapons may not be available so what you want is a good crit weapon that can hit weakpoints well.

The Nataruk isn’t a bad option for this for a budget choice, but there aren’t many secondaries that can do the job that well (most good secondaries are status-based or need their incarnon). I would actually recommend, if the Laetum isn’t available, to invest in a mob-killing secondary like the Tenet Cycron/Kuva Nukor (note that on Deimos they will work significantly worse, but should still function for this purpose on a full-heat build) and then swap out your Bramma for the Nataruk or some other primary that can get the job done.

Revenant and Nezha are great choices. If you’re having trouble using Nezha, make sure to use his 3 to survive and build a full umbral build focused on strength (and to a lesser degree, duration). Try to fit in good energy economy if you can and always keep his 3 up.

After all that, remember that Madurai will make the fight significantly shorter if you use it well. Madurai’s damage boost can end boss fights before they start, and the only issue is the cooldown/duration. If you need Zenurik for the energy economy, take that because surviving and taking 10 minutes is better than being dead, but I do recommend Madurai for quick kills.

Don’t use blast damage, it sucks. There are a few elements that you want for most builds, and they are viral/corrosive/slash/heat. Anything else is either not helpful or a worse option (to varying degrees from barely worse to not even a competitor). Deimos enemies are notably immune to viral (and this is the only area where an enemy is specifically immune to viral), so generally you want corrosive/slash/heat. Primaries with the Hunter Munitions mod can do slash well. Secondaries normally prefer heat unless they have an extremely high slash weighting. Normally, you pair slash and heat with viral, because viral multiplies damage and heat/slash are the best damaging procs around. However, since you’re on Deimos, going pure slash/heat is better as viral is useless. Corrosive is recommended for high-damaging weapons that are not good at statuses and/or can’t apply them quickly (so the Bramma would like corrosive).

Do note that Necramechs have status ‘resistance’. This means statuses are not as effective against them (they can only stack up to 4 procs instead of the usual 10 or usual infinite in the case of heat and slash), so using a high status weapon is not recommended. Furthermore, they are weak to radiation specifically rather than corrosive (similar to many bosses). Your boss-killing weapon should be modded for radiation.

If you still have issues, feel free to reply and tell me what you’re missing. Note that mods are deceptively important down to each mod slot and what specific mod is in that slot (though this should only truly be a concern in Steel Path), and you may want to put Deimos on hold if you’re trying to tackle it too early as it can be a noob trap.