Been a while, finally got some time:
I did chapter 17 yesterday night finished it today. Pretty difficult map, very well designed.
3 fronts, balance your funds between 3 fronts and each front has a purpose:
Middle: Since enemies heavily outclass you with their building bonus, they have to stall enemies as long as possible and draw as many enemies out.
I had to redo the map because my middle front collapsed, but I found a better strat to hold the middle front.
I buy additional healer and archers later, while stealing Royal Guards from Dark Gift.
Left: I build 2 archers the first 2 turns and stall for a few turns until going for a big push, two of the enemy building bonus are located here, so they have 2nd highest priority to advance forward.
Right: This is the most important front, Chloe and Flonne's team have to push as aggressively as possible, converting enemies on their way and capture the first 2 crystals asap or the boss will just overwhelm with repeated 2dmg AOE. I buy an archer and 2nd turn a scout to wall off the bottom Royal Guard as I only have enough power to convert the one near the crystal and prevent him from going after Chloe.
This is how my turn 3 looks:
Right: I sacced both spear enemies to the Royal Guards so Chloe can push the first crystal and start slowing down the rate the boss can use his 2 AOE dmg.
middle: I prepared to build wall
I saved every turn so I could screenshot more, but it's a very long map and would take a while to capture my whole strat.
