Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:6/8
K:Dmix
['A2 B cBc E3 c2 A', 'BAG FGA AFd AFd', 'BAG FGA AFA D3']  
X:1
L:1/8
M:6/8
K:Dmix
 A2 B cBc | E3 c2 A | B2 G AFD | G3 BAG | A2 B cBc | E3 c2 A | BdB cAF | G2 A BAG :| FGA AFd | 
 AFd AFD | FGA AFD | G3 BAG | FGA AFd | AFd ABc | BdB cAF | G3 BAG :| FGA AFA | D3 AFD | FGA AFD | 
 G3 BAG | FGA AFA | D3 ABc | BdB cAF | G3 BAG :|  