Amantadine did something once, when combined with sleep deprivation, weed, dxm, some benzos probably and it was very short absolutely psychedelic shift in reality.
It was nice. Seizures were not.
Memantine is actually great for providing some form of reinforcement, anxiolysis, mild trippy feelings like dxm just more clean less intense much longer acting and combination of memantine with opioids made opioids at least 2 timeas as potent ( good effects and side effects, both ).
I LOVED MEMANTINE but it is the only substance which made me psychotic without me knowong i am psychotic for quite some time and it resulted in life disaster. Now I know it just made me do inevitable unexpectedly, it just occured but same things will happen even without that psychotic mindset but it would last A LOT LONGER.
Both are damgerous so...choose memantine, much more interesting effects and no seizures.