This achievement is for viewing 435 Skits. There is a total of 457 skits in total. That means you need 95% of them. Skits are the 2D comic like scenes as well as the Exclamation points you see on your map.
This is not miss-able. If you happen to miss skits you can unlock them by completing the Bonus Dungeon and paying a Katz 500 souls per skit.