In case you've missed it, pictures like this began sprouting up across the internet (namely Reddit) around beginning of June. Look closely — to the untamed eye these might appear to be regular magic cards, but these are from the 2019 Core Set!
While this leak is not as sizable as the leaks that we had for Ixalan prior to the official spoilers, it's not everyday when we see a scenario such as this! As it stands currently, there have been numerous commons leaked, and only 3 rares. Take a look:
Sigiled Sword of Valeron (3) Artifact - Equipment
Equipped creature gets +2/+0, has vigilance, and is a Knight in addition to its other types.
Whenever equipped creature attacks, create a 2/2 white Knight creature token with vigilance attacking. Equip 3
Apex of Power (7RRR) Sorcery
Exile the top seven cards of your library. Until end of turn, you may cast nonland cards exiled this way.
If this spell was cast from your hand, add ten mana of any one color.
Prodigious Growth (4GG) Enchantment - Aura
Enchanted creature gets +7+7 and has trample.
So, nothing inherently broken or auto-includable, but what should we expect for a core set, right? This is the probable theme that we will see from M19: nothing out of the ordinary or off the wall. But this might actually play out for the best, at least in terms of some needed reprints in Modern.
I speculate that Wizards of the Coast intentionally leaked this part of the cards to this set. Why do I think this? Simply because almost all of the leaks so far were reported to be actually opened in DOMINARIA booster packs! So while it is entirely possible that WOTC simply has a packing problem, I think they decided to have a little fun stirring up rumors. Almost all commons with a few flavorful rares mixed in so far... the perfect taste, just to get people talking.