In that instance, SleepyK just let up his shield a little early (it mayyyy have shieldpoked,. Grounded hit of dair can be a little awkward, but it has almost no knockback and little hitstun, so if SleepyK reacted fast enough he probably could have shielded again (or shined, though I'm not sure I was close enough). Pretty sure my intent with that dair was just to catch him trying to jump at me after the roll (with a bair or something), and once I saw him shielding I just kinda drifted towards him and hoped I didn't get punished too hard. He got hit, and it looks like he either decided to try crouchcancelling the next hit, or he just was trying to input the next move of whatever he was going to do after shielding the downair, and just ate the dsmash in the confusion.
Basically, it's not good shieldpressure. It's not safe, and the reward is rarely good enough to justify the risk. If you want good shieldpressure, then dtilts are ok, shorthop nairs are pretty good/safe and often have followups, jabs and dsmash are decent as Phez said (though dsmash is pretty punishable if they shield the entirety), and rising uair -> falling uair can catch people occasionally. Probably other stuff, but that's what comes to mind.
