Actually, you can do it with them two wide. It's tricky, as it requires a specific order of the monsters.
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×Basically, if the top roaches are lower numbered (right click to see) than the lower ones, the group splits into 2 rows when you move down to row 17. This only lasts for a turn, so you need to be in position to take advantage of it.
In order to do it the "
proper"
way, the key to not letting them reform two rows should be obvious. You can't go south of row 15. The way you move the raft without doing that is mentioned above... you need to move diagonally.
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×The other key being that you don't need to be at the front of the raft to move it. You can move the raft SW from the NW corner.
