While this didn’t come up much at the prerelease (since there’s no real way to get rid of their +1/+1 counters in Theros sealed!), I’ve seen and heard a few players thinking that “Monstrous” is linked to the counters themselves. For example, they think that if they remove the +1/+1 counters from their Shipbreaker Kraken somehow (perhaps with -1/-1 counters) that it loses “monstrous”), and they can make it Monstrous again. This, however, is incorrect!

Once you use the Monstrosity ability (and it resolves), that creature becomes Monstrous, period. Even if the counters are removed somehow, or it gets more, or what-have-you, it stays monstrous. The only way to ‘turn off’ that monstrous tag so you can use its ability again is by having it leave the battlefield, so that it becomes a new object. So, you could use Cloudshift on your Kraken so you could tap down some new things (but the original things that Kraken tapped down are no longer on lockdown, since this is a new Kraken!)