Thanks for letting me know. The goblins cant spawn on the grass near the castle, I could try  to add something to make that more clear. 

I also gave cookie miner a try. Very relaxing and a the gameplay has a nice loop to it. I especially love the music + sound design. It took me a bit of time to realise the extra pickaxes meant I could click multiple blocks at once    

I've made an update based on your feedback. Clicking on grass shows a bit of text saying cannot summon here