silver bars mean you don't have a strong enough shovel to break it, level up some more and your shovel will get stronger.

That's probably the invincible snail from that riddle. Your time has come.

Let dastardos come and break it he'll eventually roll up and just remove the snail but failing that put a cheap fence around it to stop piñatas getting close

When? I’m level 5 at the moment

He should just appear, although if he doesn't try making a wormling ill as there easily replaced and he should appear and hopefully remove both the shelly and the worm but he essentially works as the games grim reaper *edit If he still doesn't appear your next level should give you the iron handle upgrade and you'll be able to smack the bugger to oblivion.

How do I wake up and tame the Shelly though?

If it won't wake up just let it die and come back later.

I think its needs to eat an apple seed if you want to tame it.

That thistle will also make piñata fight each other

Yes, it’s most likely the thistle that makes everyone fight. Sour shellybean drops off bad seeds, which I’m guessing is where you got your thistle seed from.

Have you tried turning off the game and turning it back on, like unironically