Printed in 1993s Alpha set, this artifact introduced a completely unique gameplay mechanic: physically flipping the card onto the battlefield
Like the first set, Adventures in the Forgotten Realms, Battle For Baldur's Gate introduces a number of new mechanics that are pointedly D&D inspired, and perhaps the most interesting of the new mechanics in this set is backgrounds
For one, theres better Horrors out there you can stick in their place but theres also not a ton of reason to be this all-in on Horrors to start with
At least, you should with a card that has such high combo potential
So if you have Summon: Bahamut in play with one lore counter, and you proliferate it twice to land on Chapter III (draw two cards), you'll also get to trigger Chapter II (destroy a creature)
and with additional copies of [casthaven]Riptide Chronologist[/casthaven], you can probably drain someone down from 21 or even 40 life out of nowhere