private static List<Item> requestedItemsList = new ArrayList<>();
    private static final EntityDataAccessor<ItemStack> requestedItemStack = SynchedEntityData.defineId(UndyingCorpseEntity.class, EntityDataSerializers.ITEM_STACK);
    private static final EntityDataAccessor<Integer> countOfItem = SynchedEntityData.defineId(UndyingCorpseEntity.class, EntityDataSerializers.INT);

@Override
    protected void defineSynchedData() {
        super.defineSynchedData();
        this.entityData.define(countOfItem, (new Random().nextInt(5) + 1));
        int randomItem = new Random().nextInt(requestedItemsList.size());
        this.entityData.define(requestedItemStack, requestedItemsList.get(randomItem).getDefaultInstance());
//        if (!this.getEntityData().get(requestedItemStack).is(Items.OBSIDIAN) && !this.getEntityData().get(requestedItemStack).is(Items.ENDER_PEARL) &&
//                !this.getEntityData().get(requestedItemStack).is(Items.PHANTOM_MEMBRANE) && !this.getEntityData().get(requestedItemStack).is(Items.PUFFERFISH)){
//            this.getEntityData().set(countOfItem, +2);
//        }
    }

    // Override to add the last hit entity UUID to the save data
    @Override
    public void addAdditionalSaveData(CompoundTag compound) {
        super.addAdditionalSaveData(compound);
        //int randomItem = new Random().nextInt(requestedItemsList.size());
        requestedItemsList.add(Items.PHANTOM_MEMBRANE);
        requestedItemsList.add(Items.MAGENTA_WOOL);
        requestedItemsList.add(Items.MAGENTA_DYE);
        requestedItemsList.add(Items.APPLE);
        requestedItemsList.add(Items.SPIDER_EYE);
        requestedItemsList.add(Items.INK_SAC);
        requestedItemsList.add(Items.GLOW_INK_SAC);
        requestedItemsList.add(Items.PUFFERFISH);
        requestedItemsList.add(Items.BREAD);
        requestedItemsList.add(Items.EGG);
        requestedItemsList.add(Items.ENDER_PEARL);
        requestedItemsList.add(Items.OBSIDIAN);
        requestedItemsList.add(Items.RABBIT_FOOT);
        requestedItemsList.add(Items.CHICKEN);
        requestedItemsList.add(Items.ALLIUM);
        requestedItemsList.add(Items.ROTTEN_FLESH);
        requestedItemsList.add(ModItems.SYDI_LEAF.get());
        int randomItem = new Random().nextInt(requestedItemsList.size());
        Item newItem = requestedItemsList.get(randomItem);
        this.getEntityData().set(requestedItemStack, newItem.getDefaultInstance());
        compound.putString("RequestedItem", newItem.getDescriptionId());
    }

    // Override to read the last hit entity UUID from the save data
    @Override
    public void readAdditionalSaveData(CompoundTag compound) {
        super.readAdditionalSaveData(compound);
        this.getEntityData().get(requestedItemStack);

        if (compound.contains("RequestedItem", 99)) {
            //this.getEntityData().set(requestedItemStack, compound.getString("RequestedItem"));
        }
    }



Current code for the data, I left it unfixed for now.