How to Beat Bosses as Jean
Jean Versus Beelzebub
You can’t avoid triggering some bleeding and armour doesn’t protect so you need some healing. The best healing is the stealth card that gives 10 health on next card draw and is 2 blue so reasonably easy to play. You are going to use that nearly always when you can so make the red counterpart a junk card. You want 2 or 3 of these. Build up to 20 or 30 delayed health repair, take that damage, then card draw.
Secondly you need to do damage and avoid taking damage from the 45 point attack. Card draws give you weakness so you probably wont do much damage from your attacks. Therefore, best bet is combination of shield and counterattack. There is a 3 blue card that gives you delayed shield and counterattack. That works well with the fact you are doing lots of draws for health reasons.
You need to get set up for the 3 blue and a good card for that is the red 1 pointer that gives shield and weakness. The weakness doesn’t matter much as you are using counterattacks for damage. There is also a red 2 pointer that gives counterattack.
Avoid the blue 2 pointer that gives 1 shield. For other fillers mostly use 1 pointers for flexibility. Getting some armour and protection red cards is okay as that gives you safety if you are forced to take damage when unshielded.
Jean Versus Abaddon
You have no way to counter the rage so Abaddon will get huge damaging attacks. In particular, the one that launches 7 attacks.
You want to launch attacks only if they do lots of damage.
So one approach is to build lots of armour or rage and then use sacrifice cards for massive strikes. Two problems with this are the remove highest buff strikes and that the deck that can handle Abaddon is not so good against many of the earlier foes.
For the first you can handle that with the red cards that give 3 protection and hope to use them so the highest buff that will be removed is always protection.
For the second, you really need the deck building node at the level before Abaddon and a good supply of shops and return facilities to keep a lean deck.
The ideal deck would have no attack cards the armour cards that you start with the sacrifice armour card some shield rage and protection cards and you would just build up to enough armour to sacrifice in one go.
Note also that Abaddon’s redraw is to add Martyr and remove your highest buff. The Martyr doesn’t really matter because he shouldn’t even use all initial and remove highest buff doesn’t matter when you have no buff. So you can keep drawing decks until you get cards you want (e.g. if you need some healing).
Also if you have the shield+weak red card then the self damage + 2 rage card will eventually only do 1 damage because of the weakness but the weakness doesn’t reduce the sacrifice damage.