6star monster and armiger

I will do so, but I am more interested as to what other pieces do I need for that team? I make Armiger quick so he can drop TM, stun the small spiders with Monster, but if I use Armiger for Tm control who will do the damage? Another Armiger if I don't get anything til then? 

Pestilus puts hp burn only on one enemy, that doesn't help. And correct me when I'm wrong, but I don't see any champ in your roster that can spread debuffs. Strategies including champs you don't have and where you can't ensure to get them in the future is not valid.

Better make planes to construct a team around Drexthar. This legendary can be obntained from the Tag Tam Bazar, so at least you know that you can get him. Start buying fragments asap, there is a limit on how many you can buy per day, so don't collect Arena gold until you could buy all at once.

Apo, Armiger, Drexthar, Miscreated Monster is allready a solid ground for a spider 20 team. The last spot should go to another champ that can hold the turn meter down, Armiger alone is probably not enough at higher stages.

You are very early game, so have some patience and wait for an aoe burn champ to round out that team.  A 2nd armiger is not a horrible idea if you have gotten other dungeons to 20, a working CB team, and still no decent burner (or CH).  MM will be useful in dungeons and DT, as will armiger.

I didn't plan to build Pestilus, only if I got debuff spread champ. Also I'm buyong Drextar fragments as much as I can, but it's a 1 year project, so will take some more time. But I guess until then I can't really make any significant progress in spider, just as I though

Actually I got Trunda for stun+aoe hp burn, but she's my Arena nuker. If I give her ACC my arena team will suffer quite a bit from that

You would have to cripple your Trunda totally, not only taking acc from the gear, but decreasing her damage as well. If the burner deals to much damage, the Spiderlings will die after a few of them had their turn. That's the reason why Drexthar (burn debuff, when he gets attacked) or Mordecai (just places the burn, does not attack with that move) are so good at the Spider.

True, didn't think about that. Then Trunda's not a healthy option

Make sure to buy drex frag daily until you get him.  He will do wonders for you.

I would focus on general progression as to short term stopgap spider progress.  Just improvinhg your gear and adding MM will help tons.

If you're not doing so already, make sure you.have a weak single.character tag team defence to help you farm points there. :)

As for Spider, Hellhades made the point that a bug.means Spider 10 gives more five star accessories than the next five higher levels so is best to focus on until you get a super.powerful team. :)