"Merlin" is certainly a magician -- but it's also the backend for OCaml's language server. It allows OCamlers to get superb editor support, such as seeing OCaml's type inference, navigating to a definition, constructing or destructing sum type values, and much more. In a different vein, OCaml multicore is certainly very interesting from a runtime design perspective -- but it also offers elegant ways to improve performance practically. It was introduced in 2022, bringing genuine parallelism to OCaml by extending the runtime with support for multiple domains (lightweight threads mapped to CPU cores). How do these two -Merlin and OCaml multicore- fit together? We've been working on improving the responsiveness of OCaml's editor support by offloading Merlin's type-checking logic to a background domain. In this talk, we'll give a small tour through that work. We'll start with a high-level overview of Merlin and of OCaml multicore concepts such as domains and effect handlers. Then, we'll explain how we used these concepts to improve Merlin's performance. You don't need any prior knowledge of OCaml to follow this talk. We hope to get you curious about OCaml and its ecosystem.