It's an artifact, and plenty of cards care about artifacts entering, leaving, or being on the battlefield
The (extremely anecdotal) numbers being passed around by fans right now are about 1 in 100 packs, however, so don't expect to open one anytime soon
Sweepers are a problem for the deck, although so far in Bloomburrow Standard, I've played way more often against Mono-Red than against Sunfall Control
You can't wait to cast one later in the turn
Not much else is known about how this mechanic will work, we can only assume from other TCGs that have this feature such as Magic the Gathering
Once Basim is protected, you can start swinging out and growing in +1/+1 counters to start snowballing from there.