he can consume his own flies and make them a fly themed item,the more quality the item has,more flies it needs:2 flies for 0 quality,4 flies for quality 1,7 flies for quality 2,13 flies for quality 3 and 20 flies for quality 4.
flysaac has a limit of 3 flies on screen,every fly themed item adds 1+ fly.
flysaac now uses spiders instead of flies,the spiders deal 50% less damage,flysaac can also consume the spiders,every 3 spiders consumed he gets 1 fly,there is also no limit of spiders.
also,there is no way that fly themed items appear in treasure rooms,the only way to get them is by consuming your flies,and you cant have the ''lord of the flies'' transformation