Definitely want to start out by building around: 

Riho (heals, HP burn, weaken/dec attack/block debuffs)

Venomage (Poisons, more dec attack, dec def and damage reduction passive)

That will jam up the debuff bar pretty much. 

Do you have a Pain Keeper by any chance, since you have a Maneater? I'm not wild about the options you'd have to go with it, but would be useful to know for the future. Feel free to show off the rest of your roster too, just in case you have any other options lying around. 

Finally got a pain keeper. So I've got Riho, Venomage, and Painkeeper. Which champs should I use for the rest of the two slots? I also got Visix now.

If you have a Pain Keeper, any way you'd be willing to try out an unkillable team?

If you could make the speeds work, you could be 2-3 key UNM/ 1 key NM without needing to stress anymore.

Here is the team I would think about building right here. The speeds will be different than the linked video I'm going to put in, but doing these speeds lets you run UNM and NM with zero gear swaps:

https://deadwoodjedi.com/speed-tunes/ultimate-budget-unkillable/

Here's a video: New Budget Unkillable - 3 Bosses, 1 Comp | Raid Shadow Legends 

Here's the slower speed version that -does- require swaps, so I'd watch the video and build the first link if you can: https://deadwoodjedi.com/speed-tunes/budget-maneater-unkillable/

As far as your DPS options for those teams, lets look at some classic choices in all the rainbow of colors: Venomage is great for Dec Def, poisons and poison explosions in Blue, seems a must pick. Aothar is a good poison champ and CB DPS in Red. Occult Brawler would be a fine poisoner in Green. 

Other champs you could look at but maybe we don't bother locking into Budget Maneater speeds are Yannica, Drex for HP burns, Bad-El. Benefits of an Unkillable team like this is that we can use champs like Occult Brawler, get them geared to hit speed and accuracy requirements, then set the team aside and just work on other stuff for a while as our team collects UNM/NM resources. :)

Sure, that would be great if I can work on an unkillable team. I went through the video and am trying to get my champs up to the specified speed. It's hard to get the maneater and pain keeper to the specified speeds without losing too much on other stats. Started farming the dragon and spider earnestly to get some good gear for both. I'll update here, once they reach the specified speed limit. 

The speed is essential for the combo to work for 50 turns. You can work on the other stats afterwards und bring up you damage. (Without changing the speed stats).

Also pay attention to the masteries you choose for your champions as some of them influence your turn meter and bring your team out of tune