In Opera 12.x there was a built in ad blocker with an option to manage the block list. There was no automatic block list update like in current version.
12.16 was the last version built around Opera's native engine. Next major release (version 15 if I am not mistaken) was built using the Chromium engine and the adblock feature was dropped.
I am glad that adblock is back, but an option to add a site to the list locally is a must.