Coldheart is a solid choice in dungeons and definitely worh holding out for. Even a pair of them if you can get them. On spider your main problem will be all those little spiderling attacks and poison stacking. It doesnt seem like much but they'll soon stack up.

You'll want to get your apothecary maxed out and get his speed high so he can hopefully top up the health of whoever is tanking the spiderling attacks. If possible try to get a shield or unkillable on your tank as well just for added survivability.

If you ever come across a bellower (ogryn tribe rare void champ) he's a solid choice when put in a stun set, pair him with scyl who is a daily reward in a stun set and they'll carry you through a lot of dungeon stages. This video is worth a watch.

https://www.youtube.com/watch?v=FZIxnefEotI

Also keep an eye out for the dark elf rare void champ "paragon". I havent tried this myself as I made it through most of the spider dungeon before I knew of this.

https://www.youtube.com/watch?v=8VeGveXC_PQ

Armiger (sacred order uncommon) is an easy champ to come across; He's in the market all the time and drops from green shards. I've heard of some newer players using him until they get other champs who damage based on enemy hp like royal guard and coldheart. As it blocks revive some people have used him in the ice golem dungeon as well.

use as many AE attackers as possible.  five is the best.  AE attacks may deprive mommy of sucking up some healing as much as possible.  i use five AE attackers and do fairly well.

adeg

Your key champ for spider is Ultimate Galek with mass HP burn. Royal guard and stag knight are in the team too.

I don't know if it's enough without turn meter reduction (Armiger or two if not Coldheart).

Should I pair UGalek with someone who increases atc or is his A2 enough? 

You should add someone who increases attack, if you have one, yes. Too hard/slow to get him to do it on his own. 

Get Armiger to level 50. 100% cr and speed of 170. No books or masteries needed. I still use him in Spiders 20 AND Fire Knight 20. HP burn champ for the spiders and a tank. I'm using Rhazin tank, you can fuse him. Also Scyl of Drakes is a beast. (free after you log in reward). I use Scyl in all level 20 dungeons. Good Luck

Armiger is available in store, or Mystery shard, whenever you see one, buy it, to upgrade skill and rank.

I am trying to assemble a top team for Spider, Fire Dragon, Ise Golem and Fire Knight

What is your best team for each,, tell me the champions, their artifacts

for example Apothecary - Speed Set

Ultimate Galek - Life Steal Set

I just reached dragon lvl 20. Rest Ist some wehre between 11-17. I focus on dragon and spider first, so I can get the speed and lifesteal set. Then I need those acc banner. 

I pulled Valkyrie this weekend. She pushed me to dragon  lvl20 on manual. I can go til lvl 17 auto, but it takes too long. 

Spider I could finally get to lvl 13 on auto. At least I can farm lvl 6 artefacts now. 

I will get an arminger for sure