Before the boss
When the battle begins, 3 Le'Boins will appear. Snache and Croco will be sent out at a slow rate.
When the castle is damaged down to about 495,000 HP, Nyalladin will be sent out, with a boss shockwave. A One Horn and Pigge will also appear.
After the boss
A steady stream of One Horns and Pigges will be sent out of the castle, and the spawn rate for Snache and Croco will speed up. Ginger Snache will also begin to appear. The Pigges are an infinite spawn, but there are only about 4 One Horns in total.
When the Nyalladin appears, never stop spamming Eraser and Crazed Wall. Use Bahamut to kill the One Horns, but don't respawn him if he dies. Once all the One Horns are dead, let the boss gets close to your base.
When the Nyalladin is close to your base, send in Island, Crazed Whale, Crazed Titan, and Jamiera. Only send one of Crazed Titan or Jamiera; if they are together, they will be killed together. Send Prisoner Cat whenever you can, as he outranges Nyalladin, even with the shockwave. Use Paris Cat to clear out the pesky minions blocking the way. Alternatively, you can use Hacker cat.
Once Nyalladin is dead, spam everything you have.