In the books
In the A Song of Ice and Fire books, the Battle of Yunkai takes place in a quite different manner. Yunkai has hired both the Second Sons - led by Mero - and the Stormcrows - led by Prendahl na Ghezn, Sallor the Bald, and Daario Naharis. Daario turns over the Stormcrows to Daenerys after murdering both Prendahl and Sallor. With the Stormcrows on her side, Daenerys orders an attack against the unsuspecting Second Sons, who are getting drunk on a wagon of wine given to them by Daenerys. While her Unsullied and Dothraki attack the Yunkish slave defenders from the front, Daario's Stormcrows take them in the rear. Almost 200 Yunkish infantry are killed while the rest surrender while the Second Sons also suffer minimal casualties and yield nonetheless. Mero, however, escapes.
The TV version does have Daenerys gift a barrel of strong wine to the Second Sons, apparently a nod to this subplot in the books.
- The Battle of Yunkai at A Wiki of Ice and Fire (spoilers from the books)