I'm not really a big fan of mixing weed with LSD, I usually end up tripping fucking balls. Not in the good way either, in the way that I start hallucinating so hard I forget what it's like to be sober. To a lesser extent it's the same deal with MDMA.
I like mixing it with any sort of pharmacutical downer though -benzos and opiates-, nitorous also works well.
Smoking while on mushrooms catapults me into outer space, I'm pretty much incapacitated.
I love it on psychedelics, E, opiates, benzos, alcohol...haha almost everything mixes well with it, except for amphetamine IMO. I can never get baked when I take adderall, its pointless trying to.
I wont take DXM without buds to combine it with. I find buds make it much more euphoric and makes the CEV more interesting.