Main deck decision for this format

Dark world is a major problem right now, and if you are get into a tournament in the next format, you should maindeck good solution against this match up.

Two Mystical space typhon:

Because shi en, ryko, lyla, sparks are not enough to deal with backrow. Sometime you need to destroy a card right away, like gates to the dark world or Skill drain.

Creature Swap:

Dark world use to leave Grapha on the field alone. Even if we can deal with him once (Dark hole for example), we still have to fight him again in the next turn. So, the best option is taking control of it. If your deck use some flooters (Machina, plants, laval, zombie, etc), you might use creature swap to take that grapha and control the field for at least until the grapha came to the field.

Bottomless:

It acomplish a better job than warning. It remove grapha, alius or excalibur. The only problem is that it is useless against shi en. But, not all the six samurai match is around shi en anymore.

good luck, and I hope you don't get dragged into the loss game