In a recent patch, Riot introduced non-unique item names, and we had to create a system for dealing with this.
Multi-instance subtemplates are common in MediaWiki; when we're using Lua, they can be much more powerful than in wikitext.
A bunch of things I did wrong because learning is fun!
The pattern of store -> query -> store -> query can lead to caching nightmares when working with Cargo or SMW in MediaWiki. This is the story of how I dealt with one.
Disambiguations are typically somewhat user-unfriendly; I describe my method for improving quality of life when disambiguation links do appear.
CharInsert is one of my favorite extensions. Here's how I made a Lua wrapper for it to create a user-friendly interface for anyone to add snippets they want.
I document my system of using hooks in Scribunto before removing it from my wiki.
A post about how to create workarounds in MediaWiki in a reasonably well-controlled manner.