YAY! My favorite kind of sandwich (right after a Firehouse Club and a Jimmy John’s Gargantuan).
Every time you spike the head in an air combo the opponent will bounce, leaving your head able and in position to OTG. If you OTG with HP (less recovery), comboing into s.MP has enough hitstun to restand. From there a slightly delayed s.MK will allow the head to recover and hit HP again and now you have a sandwich combo starter.
Another sandwich combo starter involves doing qcf+PP or qcb+KK, then OTG (or not OTG) with HP (then dash in in case of qcf+PP), s.MP, delay s.MK, HP and continue.
A third possibility is having your head in the opposite direction, chain into LP rekka x 3, OTH with HP, s.MP, delay s.MK, continue.
As for combos themselves, here’s one that I will try to record at one point.
s.MP, s.MK, HP xx qcf+MP, qcf+MP (hold HP), release HP, s.LK, s.MP, s.MK, HP XX qcf+MP, qcf+MP (hold HP), release HP, s.LP (s.LP), s.LK, s.MP, s.MK, HP XX qcf+MP, qcf+MP, qcf+MP xx qcf+PP
Another possibility is more difficult to time and doesn’t work on some characters (namely Double):
s.MP, s.MK, HP, dp+LK-LK, j.MK, j.HK, f+HP, s.LK, s.MP, delay s.MK (restand), HP, dp+LK-LK, j.LP, j.MK, j.HK, f+HP, s.LP, s.MP, delay s.MK, HP, HK, j.LK, j.MK, j.HK, f+HP, qcf+MP, qcf+MP, qcf+MP xx qcf+PP
Here’s a few things to mix it up with. After any HP that does not OTG, you can IAD j.LP xx qcb+LK for an ambiguous crossup setup, or delay a c.LK/throw for a low/throw mixup. In the corner against Peacock, Cerebella, Painwheel and Valentine, after a j.HK, HP you can dash under )if you want) and do a low/throw mixup with c.LK/throw. So it’s a cross under low/throw mixup. You can also time it so the dash doesn’t go under. After any HP or f+HP a s.LP->throw tick throw setup can be used.
edit: You can see these in action pretty much every time you play me online, so look me up. PSN is my username here, Gamertag is the same with 2010 instead.