I'd recommend waiting til you have a few max 5* champs, the node on 6.1.1 can make you take a lot of unavoidable damage so with the level your champs are at it will cost you more revives and poitions than necessary. I'd focus on taking Ghost, Warlock and colossus up to higher ranks before you try again.
Definitely couldn't hit cav myself until I had a few rank 5's. Work on event quest stuff and rank a few more champs. Warlock would be first on the R5 list if I were you.
If you are adept at dexing specials.. parry, re-parry or intercept.. you will be good to go.. also having a ton of revives and health potions, including some in overflow should help.. if you are neither skilled or have enough revives and health potion.. unitman will become your MVP (mind you it will be expensive calling on unitman).. rank 5 some of your better 5* champions.. there are numerous tips and champion suggestions.. if you don't have enough skill or lack the necessary champions, skip the challenge until you become stronger and have better skill.. then hop back and complete the story mode.
BWCV and Warlock are going to be your most useful champs. Both have pretty easy access to healing, which is important for no retreat. Warlock also works for the ST boss. They are also just really good and usable champs, so rank them up! GHulk (if you have him) works well here as the degen triggers FACE ME. G2099 (if you have her) is great for this quest and boss. She was my go to for exploration.
As others have said, it may be best to work on some other content until you have a couple of R5's.
I don't think ur roster is ready fr Act 6 except if u're okay with throwing away tons of units There's no point in trying 6.1.1 if u not gonna run through 6.1.6 to get Cavalier With ur roster I don't see that happening even if u have above average skills
Get Warlock to r5, he will be your MVP for sure. As mentioned BWCV and Collosus too. Obviusly Ghost too but before deciding to rank her up you MUST spend tome learning how to use her, she has a steep learning curve that is not for anyone ( I would know, I have her and she it is not for me)
Act 6 has many nodes with degen damage, for those lanes Mr. Negative will counter but he also has slight learning curve. Definitely waaay easier to learn than Ghost and if you do , he will be your MVP in degen nodes and any other situation where you need power control or to apply lotsa debuffs. As mentioned, GHulk and SpiderHam are the other prime degen counters of the game, but it seems you dont have them so Mr. Neg is tour bet bet in that department.
Other two options that can be very useful for you in Act 6 are Diablo (easy to learn and use) he will help in any lane/node/boss that needs poison debuff, poison immunity, nullify and all those pesky nodes that apply stun to you every X seconds or every time you do X (he has a pre-fight that makes him stun immune). Odin is also another very useful champ for any biffed up node and for his support pre-fights ( for example he can make any champ in your team basically shock immune), but with Odin you must follow a very "parry-heavy" playstyle and sp rotation to make him truly shine ( somewhat similar to Collosus' playstyle, actually) but its a very easy to learn and follow playstyle.
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As others have said, it may be best to work on some other content until you have a couple of R5's.
There's no point in trying 6.1.1 if u not gonna run through 6.1.6 to get Cavalier
With ur roster I don't see that happening even if u have above average skills
Act 6 has many nodes with degen damage, for those lanes Mr. Negative will counter but he also has slight learning curve. Definitely waaay easier to learn than Ghost and if you do , he will be your MVP in degen nodes and any other situation where you need power control or to apply lotsa debuffs. As mentioned, GHulk and SpiderHam are the other prime degen counters of the game, but it seems you dont have them so Mr. Neg is tour bet bet in that department.
Other two options that can be very useful for you in Act 6 are Diablo (easy to learn and use) he will help in any lane/node/boss that needs poison debuff, poison immunity, nullify and all those pesky nodes that apply stun to you every X seconds or every time you do X (he has a pre-fight that makes him stun immune). Odin is also another very useful champ for any biffed up node and for his support pre-fights ( for example he can make any champ in your team basically shock immune), but with Odin you must follow a very "parry-heavy" playstyle and sp rotation to make him truly shine ( somewhat similar to Collosus' playstyle, actually) but its a very easy to learn and follow playstyle.
Hope it helps.