I'm fairly sure that I don't speak for only myself when I bring up the fact that transporting mobs can be a headache (especially if the mob is tens of thousands of blocks away from your base, and tamed animals such as cats, wolves, and horses do not teleport with you.) Plenty of other servers have and currently do make use of a sort of mob pokeball type system to transport specific mobs (non-boss entities, so I'm not suggesting you allow us to move the wither, and ender dragon and stuff.) These could be customized to any sort of name or system as long as the general concept would be kept relatively the same. As for how to obtain and use these "Mob Eggs" I'll call them for now, pretty simple. A Mob Egg could possibly be found in crates or bought in the points shop and would function like a normal egg as far as throwing the egg at whatever mob you wish to transport and having the mob sort of stored inside the egg. Throwing the egg again would release the mob. The mob eggs would be one use, so I don't see them as too overpowered. The addition of this feature would make myself and likely many other players happy with being able to transport our mobs easier
i’ve seen a plugin or smth along those lines of a “critter catcher” where if you right click a mob it captures it and you can place it down back at your base or anywhere you would like (obv not spawn or places where u aren’t allowed to build)