"Like standard Mounted Troopers, these more robust mounted units are armed with close-range weapons that are excellent against slower foes. Heavy Mounted Troopers are significantly stronger, and tougher to bring down. They can also detect unseen units." —Manual description
The original Hvy Mounted Trooper for the Royal Naboo was the "Hvy Kaadu w/Royal Trooper". Like the Gungan Hvy Mounted Trooper, it rode a Kaadu into battle. In the expansion, the Kaadu was replaced with a Tusk cat.
Originally, the Hvy Mounted Trooper had 3 armor. This was increased to 4 in the expansion.