I've tried searching the forum, manual, and Google, but have been unable to find an answer. I see that the Doppelganger has a secondary attack ability in addition to the regular clone ability, but I have been unable to figure out how to actually use it in combat. Can anyone explain what I'm missing?

For context, I had the idea to protect a Baroness with a Doppelganger in the front row so I could either clone an enemy unit, or deal melee damage with a high initiative. I tried attacking a group of goblins, but I could only ever clone one of them, never simply attack them as the Doppelganger.

Thank you in advance!

If I remember correctly, the only time you can use the attack is when there are no valid targets for the clone ability (e.g. only large units or other doppelgangers available). Which rarely happens in practice.

Thank you to both StormLord1975 and QWEEDDYZ for the informative replies. I guessed that the default behaviour would be to attack if there were no valid targets, but I didn't know about the extra turn/cloning only on the first turn behaviour and didn't even try skipping the initial turn and continuing the fight to see what would happen.

Wait/defend doesn't seem to work for me; I just get more chances to clone, even if I wait several turns.

Right now? Maybe you remeber it wrong?
Doppel and Wolf Lord (another morfer) are differ. Doppel have additional turn and only at this first turn can morf himself. Wolf Lord dont have that turn, but can morf at next turns.
So for Doppel you need skip first turn to make him attack.

I tested it again. I get the additional turn if I start with Defend (Wait is initially disabled), but after that, I can only Morph, Wait or Defend on every turn. The attack only becomes available when all other small units are dead.
Same behavior in both Gallean's Return and Rise of the Elves.

DJBee, have you tested it and seen what happens for you?

Khm... im not a big fan of mods for Dis2 (too many thing i dont like even in modded dll bring fixes to ROTE engine), there is no way im miss it...

I believe I tested it and it worked for me in Gallean's Return, but I don't recall clearly as I decided not to pursue the strategy any further. It's possible I didn't actually bother to test it, but unfortunately I already finished and uninstalled the game and so I cannot easily test again. Sorry! Maybe someone else can confirm?

*Edited to remove unintended repetition*