Dogs, Dolphins, and Parrots are three of the smartest animals on Earth. This is evidence by their ability to master commands and tricks.
What if there was a simple "Teach a Trick" modal for these animals?
Let's say you obtain a block called a "Training Block". You right-click on a tamed Dog, Dolphin, or Parrot with this block. It opens up a modal (similar to a Furnace, Brewing Stand) that allows you to teach simple tricks.
1) Move any dropped items from Training Block 1 to Training Block 2
... which results in the Entity grabbing an item with his maw, traveling to the second Training Block, and releasing the item on top of the block or next to the block. Depending on which side of the Training Block the dot is.
2) Move a Specific item from Training Block 1 to Training Block 2, and a different item from Training Block 1 to Training Block 3.
... which results in the Entity grabbing the item with his maw and correctly transporting it to the designated block.
3) Herd Sheep (Dog) to Training Block 1
... Which causes the Entity to follow the Sheep entity and then guide it to the Training Block.
4) Deliver Message (Parrot) to Training Block 1
... which creates a "Carrier Pidgeon" like system over vast miles. So that players can send silly messages to each other with the Book and Quill.
5) Swim Fast (Dolphin) from Training Block 1 to Training Block 2
... which creates a path of Dolphin's Grace for the Player to use instantly.
6) Protect Training Block 1
... which would cause the Entity to defend a large area of effect around the block, and not leave their post.
What's great about this idea is that Dogs, Dolphins, and Parrots would represent Land, Water, and Air. So you could have a trained tamed animal for all three.
(Note: This would require us to be able to tame dolphins. However I would argue in making sure that Dolphins can NOT be ridden.)
Another idea is to have the Modal cost "fuel" in the form of treats. Bones for dogs, seeds for parrots, and fish for dolphins.
In summary, I think this would be a great way to showcase the intelligence of these animals, introduce a modal that could teach simple algorithms to children (if done correctly), and be a unique way to transport items.