Is it possible to do this? I tries and it seems to not update the server's data watcher...

Exactly, that's what I'm trying to do. Unfortunately I haven't been able to get my head around other kinds of packets (especially getting the data to a specific entity serverside) so I was hoping this would work. Any tutorials/ want to give me a run down of what to do. I have read your tutorial on the subject, but I had trouble.

What exactly are you trying to do?

I have the player riding an entity and while WASD+Space are pressed, do different things to variables in a third entity (depending on the combination). Basically just a controllable entity, but the entity controlled is not the one ridden.

Looking at some of my old packet code I think I might actually be able to get it working. Mostly I was hoping there was an easier way.

Are UUIDs the same client and server side? I am trying to check if the player is riding the seat, but I can't get the entity variable.

*the particular seat. I didn't want to send unnecessary packets.

why cant you just use player.ridingEntity to get the entity the player is riding?

But what do I check that against... That's what I need.

iff you are sending packets to the server for control and thats where you need the entity in your message handler you can get the plater that sent the packet using.

messageContext.getServerHandler().playerEntity

Well I did get it working, but the bandwidth use isn't optimal. Basically, any client that is sitting in a seat (instanceof ...) sends data to the server, but only ones in specific seats are needed. The entity that sends the data knows which seats serverside but as UUIDs aren't universal () I can't get that entity variable to the clientside version of it. Any ideas?

I've saved so many things to NBT that I forgot the Entity ID could be useful, good thinking! God, why did they have to make DataWatchers noob proof...

EXACTLY!!! God minecraft is stupid! Why does it have 2 different things! I meant I only use UUIDs so I kind of forgot about Entity IDs. (Note: I usually don't call to god about Minecraft's stupidness this often)

Fine, still its annoying