Unit choice and break point:
Xu : the new awakener in town, hot Caro Muma. She is a good Con stat stick, str down support, baby maker and poison trigger. Unfortunately, her poison application is quite lacking, hence need other poison team mate to truly shine.
Break point: e0 is perfectly fine, e2 is complete kit, e3 and OE are just nice add on.
Faros: I sleeped on faros for ages, but turns out, she might be the best newbie poison unit from standard banner, reason being her one cost is an AOE poison application, and it scales with number of tentacle hit. The only other aoe poison option is nymph, which is more expensive in term of card cost and provide less survivability. Also, faros just applies more poison with lower investment. Her exalt is also a nice source of shield and card search.
Break point: E0 is usuable, E2 she gets tentacle hit on strike and def, which means more poison application on the turn you play her 1 cost.
Aggripa: My favorite standard poison unit actually, she offers some single target poison application and good embryo gen. But most importantly, her exalt devour effect gives permanent alert. She's currently the only unit that can stack permanent alert, so that's that. The alert combo with her exalt shield, rouse shield, white stance is going to be your main form of survivability. She's great.
Break point: E0 is functional, E1 for better arith management and E3 for more babies.
Aigis: best free Caro support, she offers embryo gen, vulnerability, keyflare and a exalt stun, the GOAT of free units (obtainable for free by beating chapter 1)
Break point: E0 is already complete, E1 for baby gen with strike, E3 for even more babies.