Semi Aquatic mob

Just set your mob to aquatic, then in ai tasks go to "movement tasks" find "swim in water" then put it in your ai tasks. Hopes this helps :)

that doesnt help because that setting doesnt even exist-

For anyone still trying to figure this out, I found an easy solution to making a mob that can swim and walk on land (kind of)

• Creating your entity
  • Create the entity, add the model, animations, etc, whatever you want it to be
  • Make sure your entity is immune to drowning in the behavior tab
  • Do NOT tick it as a water entity, this will remove its ability to effectively walk on land.
  • AI and Goals
    • Wander Around Randomly
    • Float in Water
    • All other tasks you want this entity to have can go in between or below.
  • Triggers
    • Create a new OnEntityTickUpdate procedure
    • In this procedure you will do the following:

      • If is [Event/Target entity] in water 
        do
        	Add potion [Dolphin's Grace] with level [1] ticks ambient [false] particles [false] to [Event/Target entity]

  • This will make your entity float at the surface of the water constantly, but it can still swim and walk on land.
    • You can make conditions to make it so that the entity only floats if it is moving. You will have to check to ensure that at least one of X or Z delta movements do not equal to zero.