Duelling against magical creatures all comes down to your duelling proficiency. The same rules apply. Knowing your opponent is still important, just as in case of a human opponent. However, creatures are likely to have more diverse personalities, as they belong to many diverse species, while humans belong to only one species. Seeking knowledge will help in either case. I would specifically warn you against the basilisks and the cockatrices because looking at their eyes directly can cause instant death and indirectly can cause petrification. Also, basilisks have venom and cockatrices are fire-breathing. Then I would warn you against the Chimaeras, as they are equally dangerous. Then come the inferi, the acromantulas, the dragons and then also the trolls and giants. We have discussed in this book until now, which spells are effective against which creatures for many creatures, but still there are many more.

Magical creatures can be used in combat, that is as offensive provided you can control them or defensive, and can also be used by others to harm you. So get to know magical creatures and be prepared.

Something as simple as sending a fwooper to your opponent could make a lot of difference to your opponent or foe. A fwooper's call without the Silencing Charm on drives the listener to insanity over time. There you have it, an example of how you can use a fwooper in duelling.

Knowing simple things such as a phoenix's tears can instantly heal most injuries and be an antidote to basilisk venom can help you on the field.

So perform your research and make the best of it.