Chain Combos are combos in where weaker strength Basic attacks are cancelled into stronger strength Basic or Command Basic attacks. In games such as the Darkstalkers series and Marvel vs Capcom series, Chain Combos are sometimes known as "magic series".
In MUGEN, coding the ability to perform Chain Combos is done just like any other cancel, using a ChangeState controller;
[State -1, Standing Medium Punch]
type = ChangeState
value = 210
triggerall = command = "y"
triggerall = statetype != A
trigger1 = ctrl
trigger2 = stateno = 200 && movecontact ;<-- allows the move to be cancelled from Standing Light Punch on hit or block.