I have done this once, I had a rather large dose of acid followed up by 100mg of mdma at a 4 hour mark of the acid trip. I would argue that it is essential that you dose mdma hours after taking the lsd for the best experience, many people seem to find 4 hours of wait good but I think it could be taken a bit earlier too. The thing they say is if you take both at the same time, you might not have a pleasant experience. First, you get the perhaps tricky coming up phase of both lsd and mdma both at the same time. Then things might start to get confusing while they sort of fight for the effects. Lastly, the drugs have quite a different duration, if you take them at the same time you will be coming down from the mdma while still peaking on acid which atleast to me doesn't sound fun. It's a problem though, if your drugs are irreversibly mixed together.
Personally on my trip, I was having a hard time with the acid. Things started to sort of breaking apart for me mentally in a schizophrenic manner. I felt confused and couldn't focus on anything, conversation with friends was impossible and basic mechanical tasks like weighing mdma crystals on a mg scale was next to impossible. It was only getting worse too. Then the alarm on my phone rang and I realized that it's time to take the mdma, I had made up my mind about doing this even before taking any drug that day so despite my really difficult acid experience, I took 100mg mdma. Thank god I did. It's hard to explain exactly what it accomplished at that time, it was like it completely cured my schizophrenic adhd state of mind and turned me into a zen monk capable of having these most amazing and deep conversations, it was full on psychedelic bliss, calmness and clarity! The stimulant effect on the brain was really pronounced. It really surprised me though, that mdma saved me from my idea of a bad trip when conventionally people seem to prefer benzos or antipsychotics as something to "abort a trip". Had I taken an anti-psychotic I probably would have been more fucked up mentally and less able to form a sentence in my head on top of being very restless.
Anyway, not too long after taking the mdma (surprisingly short as a matter of fact) I crashed really hard. Worst comedown/crash of my life. Next 24? 48? hours were basically spent crying in bed at a time when it was totally not ok to be just lying in bed all day. After this difficult experience I concluded lsd, maybe most tryptamines in general are not for me, atleast when taken alone. I really love psychedelia and tripping, but my brain just seems to be wired in a way that I often experience these substances in a profoundly uncomfortable manner. Gonna stick with phenethylamines from now on.
This is my experience with LSD + MDMA