With the update of 7.10e, after reaching wave 9 on Insane Survival in any map, monsters and chests have a chance to drop Super Loot. This was also added to the shop and pure strategy modes in 7.11. This loot has generally higher base stats and more upgrade levels compared to normal loot. According to Trendy, Super Loot usually has better stats even compared to boss and challenge equipment.
With patch 7.12, and the introduction of Uber Monster Fest, Mega Super Loot is available.
Each wave past 15/16 has a higher chance of having better Super Loot. Wave 25 will have much better Super Loot than wave 20.
When Playing Survival with Hardcore Mode (does not apply to Pure strategy mode) items dropped will be better, same goes to Mixed Mode. When both Hardcore and Mixed Mode are checked, loot will be far better than on normal Survival.
Also the higher campaign map you play the better items have chance to drop, for Example on Summit map items dropped on wave 15 will be comparable to items dropped on wave 18+ in Deeper Wall. Of course higher difficulty will get you better items.
Mistymire Forest Nightmare Survival has a chance to drop Godly items with high stats (can even go above 360, current cap) that normally appear on Mythical items.
Currently, Super Loot is NOT available to console players. However, loot with 50 or more upgrades is considered "Super Loot" to most non-modded players. Loot with 50 or more upgrades are found in the tavern, or in chests. "Super Loot" is mostly found in the tavern after levels such as The Ramparts, Morrago Desert Town, or Aquanos is completed. Most "Super Loot" is found on Insane+. The best armor piece has 255 upgrades, however no armor piece like that has been found.