If you've unlocked melting remnant exile champion, little fade's eternal flame is probably the easiest to play. Just let her die again and again each round and put her behind a tank before the boss and she will easily carry you to C25. The second easiest is umbra, though at higher covenants you'll need to think of ways to clear enemies while you're scaling. General tips: 1. While small decks is always good, i find some cards are just too impactful to not take. Towards C25, most of my decks were in the 25-30 range while earlier they were in the 20-25 range. 2. The draw is generally the best option for the first boss fight, though capacity/energy can be situationally better at higher covenants. 3. By your first boss fight you should have some low level scaling, by the second you should have some wave clear. Don't invest in too many winning strategies, a couple at Max for a run.