My way of passing Oki Islands 1001 (ends on 5/5/2024)

The boss rush is super challenging and luck/strength based. Just finished the last boss at round 29 as a free to play account. I want to write out the lesson I learned to help others! 
You need 18 different general + units, and forget about morale reduction, the challenge is designed in a way that it's not worth it. This challenge ends on 5/5/2024

Boss 1:

Special: receive melee damage reduction, 3 round cooldown lightning special attack that deals delayed 1200 true damage, but damage can be shared.
Useful unit:
1. Shimazu: Enable another attack from hardest hitter, stack active skill plus 1 set to shorten the cooldown
2. Date: hardest hitter, high chance not being countered
Method:
1. Use all teppo, you won’t need them for the next two bosses.
2. Most important: melee attack includes ranged unit attacks right beside the boss! So KEEP 1 GRID AWAY from the boss when attacking! I stuck here for so long using teppo to surround boss and fire in the face for morale reduction. The damage was too low there!
3. When lightning is marked, if the unit is important, have at least one unit beside it to share damage, otherwise it’s pretty much instant kill. It would be ideal to have more than 1 unit around the marked unit, in case the damage sharing unit is killed by boss in the next round before lightning hits. (I think more unit around the marked unit, the better the damage distribution)
4. No need to drop morale, since you need to sandwich the boss to drop it, and that means doing ineffective melee attack.
5. Somehow boss prefers to put lightning on the unit top left for me, so consider putting your weakest unit there when boss expect to summon lightning.
6. If the lightning marked unit is weak or low hp, drag it away from everyone else and let it deal its final blow
7. Spread out unit to prevent the normal attack splash damage.

Boss 2:

Very luck and strength based.
range damage reduction. When ninja support arrives, takes no damage. Special attack can damage adjacent unit, guaranteed 2 normal attacks each turn

Useful unit:
1. Yagyu: 1 damage from enemy for 1 turn during enemy’s turn. You can use it to gamble on boss hitting this unit in the next turn.
2. Nobutsuna: Hard hitter with sword master. If 4 star, fanatic guaranteed with active skill
3. New unit musashi: I don’t have that general but I assume it could be helpful since he activate a powerful bonds among two units above.
Method:
1. Ideally use yagyu on the turns when boss special attack is ready (like the first attack)
2. Use at most 3 units staggered when special attack is about to hit.
3. Count the enemy hp for the 3 ninja call. Move and attack one unit at a time. If most units have finished attack around boss, and boss’ hp is close to next ninja call, consider saving special attack to next round. This way units can counter this round or use special attack then leave next round to trigger ninja and avoid additional damage next round. Obviously if that unit's hp is low, use the special attack when you have it. Remember all units that have moved but have not attacked beside the boss, and all counter will be wasted if ninjas are called during those time.
4. If some units are not involved in the attack, consider stationing at the ninja spawn place to block the spawn. The ninjas are weak but it takes time to kill them. We need to save special attack for boss and more rounds for the final boss. Location of ninjas attached below.

5. If unit is restrained, they are doomed and should attack first(assume ninja is not called). Sometime it might be worth it to activate special buff for Yagyu to save the restrained unit ( ex. if only nabutsuma is restrained, since he would likely die in next round).
6. Always the best to have all 3 units attack together. Not advised to save rounds to finished off ninja in the same round and only left one unit to hit the boss. Wait a round instead.

Boss 3:

Ignore teppo damage , 2 grid counter, delayed 1 grid sweep.

Useful unit:
Hojo, Ottmo: strong war gear general with speciality unit
Honganij: strong war gear with heal.
Sassa or other disable counter general: useful to let non war gear unit to get free shot.
Burst attack unit like Ieyasu: max output with fewer counter attack from boss
Other healer: enable non war gear unit to attack more often.

Method:
1. This is usually just a race against time. Put all support unit (healer, disable counter) on war gear so that they can do a few free shots while special buff is recharging.
2. I use a combo of archers and war gear only for this to avoid boss attacking me actively. But the strong unit left in this round is usually sparse so you usually can’t be picky.
3. Pick the right time to attack for non war gear unit. Aka only when boss under negative buff and not having boss attack up buff
4. Watch out non war gear unit health from tower attack and flame. Also don’t waste attack on tower.
5. Last round is when you finish round no.30.
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Tips:
Upgrade gear and unit, sell exp and low tier items for money if needed.
Try to get early tier rewards first.
Keep trying! Sometimes one critical attack could mean a different outcome! Good luck!