Basically, for some reason, my friend had a villager to trade 3 Emerald Blocks and 5 Diamonds just to get mending. We searched on the web and don't think that Emerald Blocks should naturally be traded with a Villager to get mending. Nor should Diamonds either. Also, my friend got another villager with mending that needed 10 Emeralds and 5 Acacia Logs. Which is weird why Acacia Logs would be used to trade with at all.