Already unlocked 3 Quests when continuing my stored save game, but you need to restart fresh for the first Quests that are easy. They only unlock when reaching certain calibrated points in the game. =)
I finished it with 3 'support' and 3 'wall' knights. Focus support on the dark knight and use wall knights to bring the other two enemies down one at a time. There's a considerable decrease in dark knight's area (Debuffing) attack if one or more of his companions are dead. I also used the final strategic formation 'Marauder' along with HP, Block and Attack equips for all six knights. As for arcana, clean air is a must to remove bad status effects. For the other two, I used holy bastion and sun strike. Maxing the three arcana to reduce their cooldown also helps a lot.
@leedade - The final knight is in Arcane chapel (the area where you first fight the dark army). Just win the fight and you will get the egg.
@Yahel007 Maybe that's why it unlocked for me at 10 knights, I had actually previously hatched some knights in a my first game but restarted for the quests.
And yes MrDayCee the 10 knights for me was including the Miner Knight, I was missing the monk knight which I got from the arcane chapel at the end, but it unlocked for me when I got the witch knight, which for me was the 10th.
Eggcellent si not bugged. It just counts your eggs with all games you´ve played. My quest was finished with the 9 eggs but the remaining 2 eggs were cracked before so together it makes 11.
That very well could be the intention for Eggcelent, but the quest text says "Get all 11 Egg knights", not "Get 11 Egg Knights across all playthroughs", so it's either bugged or the text isn't correct.
The Dark Knight can be defeated laughably easily by 4 steps:
1) Get a couple knights with Dragonborn (preferably multi-hit ones)
2) Put everybody in Astral Assassin strategy (gives everybody poison +5).
3) Stack Poison +5 on every knight (can be farmed in the slime cave if you don't already have enough).
4) Stack attacks on him. It doesn't matter if it does 50 damage or 1 damage, every attack will stack the poison. I had poison 685 on him before he finally died.
Poison is ridiculously overpowered because it stacks so easily. There's a +8 poison wand available for 250 gold that I used to stack over 800 poison damage on the Dark Knight.