Maybe they’re confusing macro and mega? If not, I couldn’t tell you.
Try searching for Megaloceros. Megaceros is an old term.
I’m not really “into” mammalian mega-fauna, but the brontotheres and uintatheres were pretty cool. For example, Eobasilus (about a third of the way down - the knobby-headed rhino-looking fella), and Arsenotherium.
As far as big deer like Megaloceros, Eucladoceros was pretty cool.
Glyptodonts, such as Doedicurus, look pretty spiffy with their morning-star-like tails.
I bet all the other proto-elephants laughed at Platybelodon (second picture).
I’ve always been partial to brontotherium.
What a great beast of war it would make! You could ride its back and use its unique nose piece (combined with an industrial-size rubber band) as a slingshot launcher!