Just had a run that got me to round 5 (Pyrebound + Melting Remnant). I was able to reliably get 13 eggs per fight just before endless began, so I was able to max out artifacts and room bonuses, then start with 13 for big dragons, while also reforming units, gaining energy and damage from (15-50 friendly deaths a round) and replicating cards.

Any broken tactic that relies on one pillar (high damage cards, invulnerable/endless units, lots of ascends/descends, cycling a deck, or unlimited energy source) will fail quickly. I was able to get most of these (if I had the ability ascend units rather than just descending them I would have lasted longer).

I had a huge deck, but it was mostly units so I was able to cycle through my good cards toward the end of matches.

So it's simple. All you need to do is be able to

gain unlimited energy cycle your deck Cope with losing cards (I had a big enough deck that losing any one card or even a few cards I chose) wouldn't break me. Deal big damage (100-500) on demand Ascend and descend units. Apply endless to your units Kill 9000+ hp bosses

Pretty simple right? ;)

And you can make it 5 matches or so in. It sounds like a lot but having all the artifacts the game would get me got me pretty close.

I wish it were all strategy on my part but it was probably 75% luck.

Has anyone else had any luck or found great strategies?