About the scorpion boss:
Equip a necklace that prevents stun, and always keep your HP full. Use one unit to heal, cleanse, and support, and one to attack.
Take it slow — don’t rush by using two attackers, or it’ll take much longer to win.
The team with the higher level attacks first, so if you’re level 41, you’ll get the first move and a solid advantage.
I didn’t quite understand the part where you said you still have enough blood to consume — maybe you meant HP?
Also, level 21 is still too low; you really need to be at level 41 to have a proper edge.