Here is some guide I created long time ago, ofc. there might be more up to date information:
To copy a mob, you need to do the following steps (put the results to excel to change stuff):
1. Query mob ID by codename of mob in RefObjCommon
2. Query RefObjChar mob ID by using Link from RefObjCommon (last column)
3. Add different skills for skills 1 to 10 in RefObjChar to use different skills on mob (need to match animations, LY = three animations only)
4. Query Tactics ID in RefTactics by mob ID from RefObjCommon
5. Copy your new information to the tables in your DB: with new RefObjCommon ID, new RefObjChar ID, new RefTactics ID, ofc. they need to be linked
6. Use DB2Media tool to generate media entries, for chardata text files
7. If you did not add new Skill IDs, you do not need to add anything to skilldata files
To check for the animations, you need to use the skilleffect file (browse with notepad++ and search for all lines). Usually there should be skills on mobs with "ANI_ATTACK1", "ANI_ATTACK2" and so on. These need to match your new skills or you do not see any animation ongoing.
I attached a quick query to catch (almost) all information for specific mobs by given name. Make sure to match the skillnames too.