Achak looks like a good choice, especially for Spider. Royal Guard, Bellower, Fayne, Aox, Cillian could also help - all more useful than Tallia, I think. 

For your arena team, I don't see what Vergis is adding, why don't you use Stag Knight who is very valuable? 

Since I don't have a speed lead, my team usually goes second. Vergis has a shield set so they actually survive to the second round. Stag is built with a lot of accuracy and I loove him in dungeons but he usually doesn't make it to the second round in the arena. 

One thing you may want to consider - you have almost all of the necessary pieces for a one-turn kill on Spider 20.

My personal team is Gurptuk Moss-Beard, Rugnor Goldgleam, two Royal Guards, and Coldheart, but basically all of those pieces can be replaced.

Instead of Rugnor, you can use Fayne to place the DEF down and Weaken debuffs. You have one Royal Guard and one Coldheart, so the missing pieces would be someone similar to Gurptuk (BEK, for example, would also work) and another MAX HP champ like RG and CH, or simply two more MAX HP champs. You may even be able to pull it off with two Armigers.

It might be a bit early to be working on these, but given you mentioned Spider as your limitation, it might be worth maxing your RG and CH in preparation.

Thank you for the suggestion, I actually have 3 CHs, but only one is rank 6. I think I'd rather get RG to 6 first before I work on another CH, but Fayne I didn't even consider as an option. I thought I'd get to 20 if my support was strong enough but maybe I should've focused on Max HP damage more

Yeah you should be able to get the one-turn kill with Fayne, 3 CH, and RG.

Unfortunately CH is suboptimal for this because of the AI - she uses her A2 first, which means you need her at 190+ speed in order to get her to act twice before the mini spiders get a turn. So you'd need all three of your CH at 190+ speed. Your RG and Fayne can be 170+.

In terms of stats, you'll probably need at least 200 CD on each of your damagers, and of course a guaranteed crit - though bear in mind CH gets a nice crit bonus on her A3, and RG gets a 15% bonus as well due to affinity bonus.

Also, you might have trouble on the earlier Spider stages (17-19), due to weak affinities - on 19, for example, your RG will basically be useless, so it might take a few tries before you get your crit to land for the kill.

Thaaank you! I will definitely work on all of that! It would be awesome if they added the choose your AI option before I build them lol

Tallia  is  insane  Arena  Nuker.

Tallia  A2  hit  is  comparable to  a  SkullCrown level  of  damage  for  Epic.

Players  have  looked  at  her  Damage  Multipliers.

Tallia  should  exceed  Elhain  Damage  by  alot.

If  you  are  not  seeing  a  difference,  It  means  you  have  done  something wrong.

What  gear  do  you  have  on  Tallia?

Did  you  book  Tallia  A2?

Dio  you  have  Masteries on  Tallia?

Are  you  using  her on  a  speed  arena  team?