Survival Mode 21 is the same as normal 21 except for two things: you need to go through 5 opponents instead of 1; and your hand doesn't recover after you win a match.
Since the rules are the same I'll just provide you with some tips that I've learned while playing.
- Since the deck is shared trump cards are a more important part this time. It's in your best interest to hold on to as many trump cards as you can so that when something goes awry you can correct it.
- Hold on to trump cards that allow you to search out specific cards as it makes it easier to get closer to 21 in a pinch AND helps establish your opponents face down card.
- Shield cards are a godsend in this mode! When you realize you're over 21 and have no way to return a card, activate a shield. The blade will lower and you get to keep your finger regardless of if you lose or not. This even works when you're betting only 1 finger and can make it easier to win without losing any fingers at all.
- As you play you will unlock more trump cards. The full list can be found by pressing pause and going to Rewards. There are 15 in total and I unlocked 5 of them after beating the 5th opponent but you receive them regardless of if you win or lose. You also win them in Survival+ but you need to win Survival before you can unlock it.
If you need any additional info, explanations, or tips leave a comment and I"ll add more.