The Boar Knights were rental monsters that had been on discount when Jin had first accessed the Dungeon Maker. The knights were similar to Nyanmi but the rental cost of Nyanmi was equivalent to ten of these boar knights.
Jin initially thought that getting more rental monsters would bring more variety to the table. However, his funds were severely limited by the decision he made in the Dungeon World so he had not touched any rental monsters for the time being with the exception of these boar knights and Nyanmi. Nonetheless, it was a good idea to increase the variety. Jin also wanted to buy the Boar Knights outright like what he had done with Nyanmi but for some reason, he never felt any decent connection or bond with them, so he decided to just keep them as rentals.