Raid boss, basically when you get it down to half health unblockable missiles are fired at you, and then at low health snow starts falling that freezes you. So after multiple attempts, and finally getting to low health with player 1 that happens.....
Keep in mind you have to play this mode if you actually want to unlock shit and get coins to unlock shit in krypt, and it's being panned for being frustrating and unfun already. Also have to grind consumables to make these challenges more bearable, but you need to do towers of time for money to being able to get chests with the consumables....... Oh, and some challenges require you to have select consumables or otherwise they're basically unbeatable.... Some require you uppercutting 50 times in a tower.... Hence the evening in a nutshell....
The vid will make more sense after more people at neogaf get the game, since expect to see a lot of people unhappy with towers of time.....
Edit: This vid sums up towers of time nicely....