Here we have another large omission that took place when Oliver Cowdery initially copied the text from 𝓞 into 𝓟. In this instance, Oliver may have caught his error almost immediately since the level of ink flow for the supralinear insertion appears to be unchanged. The length of the omission is close to being another whole line of 𝓞 (perhaps 𝓞 had a minor crossout in this line). There seem to be no identical words that could have led to a visual skip here. For two similar examples of what appears to be the omission of an entire line of 𝓞, see above under Mosiah 17:2 and Mosiah 18:28. In those two instances, the level of ink flow is heavier, which suggests that those corrections were made while proofing 𝓟 against 𝓞. In any event, the added line here in Mosiah 18:35 was clearly in the original manuscript; Oliver would never had added such specific information to the text, especially when there would have been no independent motivation for doing so.
Summary: Maintain Oliver Cowdery’s supralinearly inserted line of text in Mosiah 18:35 since this reading must have been in the original manuscript.