Rideable entities disguised as other entities can be ridden but not controlled.

[James103]

To reproduce:

1. Starting with Minecraft 1.16.5, install Fabric loader and Fabric API.
2. Install mobdisguises-1.0.0-fabric and disguiselib-1.0.2-fabric.
3. Create a new world with cheats enabled.
4. Find a horse and tame it.
5. Give yourself a saddle and equip it on the horse.
6. Run /disguise @e[type=horse] as spider (optionally replacing spider with any other non-horse entity)
7. Click on the (disguised) horse to ride it.
8. Try to control the horse.

Issue on MobDisguises end: samolego/MobDisguises#4

[Patbox]

This is more or less limitation of Vanilla client. But it could still be somewhat worked around

[James103]

This also happens with Striders:

1. Starting with Minecraft 1.16.5, install Fabric loader and Fabric API.
2. Install mobdisguises-1.0.0-fabric and disguiselib-1.0.2-fabric.
3. Create a new world with cheats enabled.
4. /summon strider
5. /give @p warped_fungus_on_a_stick
6. /give @p saddle
7. Use the saddle on the strider, then ride it while holding the Warped Fungus on a Stick.
8. Notice that the (undisguised) strider can be controlled properly.
9. /summon minecraft:strider ~ ~ ~ {CustomName: '""', DisguiseLib: {DisguiseType: "minecraft:player", DisguiseAlive: 1b}, UUID: [I;-1075014358,-807843482,-1879089003,1077279333]} (summons a Strider disguised as a player)
10. /give @p saddle
11. Use the saddle on the (disguised) strider, then ride it while holding the Warped Fungus on a Stick.
12. Notice that you can't properly control the (disguised) strider (it does not move while being ridden by you).

[samolego]

I believe that will happen with any entity that can be ridden but disguised as "non-controllable" (e.g. boats, minecarts disguised as other mobs ...), as entity riding is done by the client afaik.
That's also why hacked clients allow you to control llamas / horses without saddles (if I know correctly).

[James103]

Fabric Carpet mod already shows that server receives movement inputs from players, in PlayerInputC2SPacket (more specifically at least p.getSideways(), p.getForward(), p.isJumping(), p.isSneaking() where p is the player), and various public servers that have rideable entities make the entity's movement server side. This would theoretically allow for any entity to be rideable and controllable server-side as long as it is actually a disguise of a rideable entity. Could this server-side controllable entity movement be implemented in DisguiseLib?

[samolego]

If I find a way, definetely :). Thanks for the examples.

[James103]

I can still reproduce both problems using MobDisguises 1.0.4 and DisguiseLib 1.0.8 on Minecraft 1.17.1.
In addition, disguise @e[type=horse] clear on a nearby horse does not make the horse controllable until you reload the entity.