So my basemap is a world Mercator projection and in wfs format and I'm trying to put a WMS overlay in a different projection over it? Leaflet's API didn't give me much info on changing the epsg so is it even possible?
Leaflet supports PseudoMercator projection out-of-the-box (EPSG:3857). You can force Leaflet to use a few other projections listed here in the documentation. Don't worry, I found leaflet's API documentation kind of 'meh'. Documentation by programmers...
World Mercator is supported with a easy to use method, lucky you.
You just place that anywhere in the global scope of your script and it should set your projection for you map.
Additionally, there is a plugin for leaflet that can allow you to use more 'uncommon' projections. Proj4Leaflet
Note: It doesn't appear that Leaflet will tranform your layer into another projection like ArcGIS or QGIS but will just take the data at face value and render it that way. You will need to serve your data in the projection that your tell Leaflet to use.