To connect your old Spine 3.8 assets with the new Phaser + TypeScript setup, you might face some challenges due to version incompatibility, especially with features like mesh deform. Since the official spine-phaser runtime is compatible with Spine 4.1, you may need to consider upgrading your assets to a version that is compatible with the runtime you are using. However, if upgrading is not an option due to the loss of contact with the artist and the presence of mesh deform, you might need to explore using a custom solution or modifying the existing runtime to support your specific needs. Unfortunately, without the ability to upgrade or modify the assets, integrating them seamlessly with the latest Phaser setup could be quite complex.