@Sidnas2 I'm was having the same issue and found a solution that works till several stages on T2. Upgrade Samurai as much as you can and make sure to Attack the T1P20 with fully charged cube, as the samurai upgrade adds damage based on your max damage.
@Kosh67 I'd say, it's a common sense to read the skills of new characters and enemies... even the game tells you to do that at some point with the tips.
@SataiDelenn There's a requirement to unlock high-tier packs. it written on the deck in store(you have to mouse-over on them):
Silver: Max all commons -or- make any purchase.
Gold: Max all Scarces -or- spend 100 Kreds
It took me more time than I'd like to admit to figure out Level 18 and was getting really frustrated. After realizing my mistake, I passed it with a first try.