Luis_ST

it's the place flage of the Block, you can look at Constants.BlockFlags for more infos about possible values and what they does

i've test your code and unfortunately i can't tell you what'S exactly is the problem the only thing i can tell you is that HalfTransparentBlock#skipRendering is not called, but i don't know why sorry

you need to call Level#setBlock to replace the Block in the World

post a git repo so i can debug this local, since your code looks okay it should work

show the Registry Entry of your ColoredSlimeBlock

post full debug log

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you need to register the Block itself and the BlockItem for it

which class/package is relevant or where should i look into?

this is the Item Registration

create your own Thread, post debug log

show your Block Registration and do never use @OnlyIn it's only for vanilla

you can use ItemStack#getItem to get the Item, then check if the Item an instance of ArmorItem. then use ArmorItem#getDefense to get the Armor value

show your Block class and your Registration