Mormon tells us that the Lamanites used intrigues of their own to entrap the Nephites. After noting that in verse 27, he gives specifics in verses 29 and 30. The Lamanites attempted to use the cover of night to surround the Nephites, but this tactic did not work. Rather, the Lamanites lost men. Secondly they attempted to use the trick of getting the Nephites drunk, a trick that does not work.
Textual: We do not know how many intrigues the Lamanites might have used, but Mormon records only two of them, and it appears that he selected those two carefully. Both of these intrigues are methods that Moroni has used. The surrounding by night was the key element in the retaking of the city of Mulek, and the administering of wine was a key to freeing the prisoners in Gid. The Lamanites clearly found out about these tactics and attempted to use them against the Nephites. Because Moroni had already used them, he was aware that they might be used against him, and he was ready.
Mormon tells us these two specific examples because they were the same tactics as used by Moroni, but with different results. What Mormon wants to highlight is that it is not the stratagem, but the quality of the person that made the difference.