To unpack it in simple terms, this Grixis (Red, Blue and Black) creature has the ability to copy instant or sorcery spells that target just one player or permanent and use the new copies so that every player at the table (except you) gets hit instead
Black doesn't have many of these, but cards like M.O.D.O.K., Evil Intellect, Gixian Puppeteer, and Construct a Cosmic Cube all pair nicely with a Night's Whisper
2020-06-23 Massacre Wurms triggered ability triggers if a creature an opponent controls dies for any reason, including from its first ability reducing its toughness to 0, as long as Massacre Wurm remains on the battlefield
It can also win games using Jeskai Revelation instead of Monument to Endurance
TLE includes around 300 different cards, including new cards and reprints
It then provides you a method of getting those counters by pinging creatures