is it possible to add new items or blocks with sponge plugins like mods?
Stuff like blocks or items need to be client sided in order for the client to recognize them as blocks/items. Unfortunately Sponge is only a server side API
There is the possibility to make a hybrid plugin/mod that interacts with SpongeAPI and yet still uses Forge for adding custom content just the same. Almura is a pretty good example, and @Zidane can say more about how it works out.
What about one that uses a vanilla material but has different server side properties? That way you could make it interact differently, or maybe even (although it’d probably have to be on the client too) you could use a resource pack with custom block states to add new blocks for different data values that the server could make work instead of automatically getting set to 0.
There are a few bukkit plugins that ‘changed the properties or select blocks’ by storing the blocks location and then checking on playerInteractEvent. There is nothing stopping you from doing that with Sponge.
As for changing the resource pack to change these blocks with the custom properties … That isnt possible unless you had client side mods/sponge plugins due to the fact the server doesnt really interact with the resource pack
Actually, it’s possible for the server to send a resource pack to a client.
No i didnt mean it like that. I knew you could send resource packs to the client. I meant for the resource pack to load the texture of the blocks with the custom properties and keep the normsl texture of the block too for the blocks the plugin doesnt interact with.