I second the OP’s request for a means to practice combos but I would prefer a more specific implementation. (See below.)
I have never been able to deliberately complete a combo. The Warfare perk “Chain Strike” will let me see when I have enacted some portion of a combo sequence but it is almost always by accident. Enemies die or become debilitated too quickly for me to get much practice out of them and they are too few and far between.
Bernard would make for a perfect training dummy except for one thing: he is too defensive. He is always on the lookout for me doing anything even slightly fancy or ambitious, then immediately punishes me with an interrupting attack or a master strike riposte. I can get the timing, I can get the speed, but he just refuses to let me witness the whole flow of combo swings from start to finish.
~ ~ My request, then, is for Bernard to have two training modes: the Normal mode he has now where he is very defensive to the point where a fight may last indefinitely, and a new Easy mode where he is less defensive (ie. does not attempt to interrupt or riposte you) so you can get a sense for the flow of mouse movements necessary to enact a combo sequence.
This may be a segue to a larger discussion (or at least my ranty 2 cents to the devs) but the reason I have never been able to deliberately do a combo is because I am never able to maintain confidence concerning what mouse movements constitute which weapon movements, therefore I have never been able to dedicate combos to muscle memory. The 5-pointed star is so unintuitive and so lacking in feedback. Half the time I think I need to be sliding my mouse down and to the right to hit the right leg, then the other half of the time I think I need to be sliding my mouse up and to the left to hit the right leg. And do I release Left MB when I am still in the backswing or when I am committing to the forward attack swing? The aiming star is so ridiculously bad on so many levels. I have 490 hours in this game, more practice hours with Bernard than I can possibly remember, four different playthrough save lines (all in progress), yet I still can’t do a weapon combo on demand. It’s frustrating beyond words.
…If you’re now wondering how I defeat enemies, my answer is: master strikes (defense is your friend), clinch cheesing followed up by stab damage (I like using maces with a high Stab stat), or, occasionally, either overpowering or out-enduring an enemy until a lucky blow from me manages to turn their shoulder/back, then I exploit that opening with as many frantic unaimed swings as I can manage to fit in before they re-raise their shield. It’s not exactly elegant. I would much rather do a combo.