How do you crack the purple rocks?

Well, when it comes to the purple rocks, you have to upgrade your pickaxe to the enhanced pickaxe (to make it, you need x7 diamond fragments, x3 Mysterious parts and x1 wood)...I think you get to unlock this through a random event or it's automatically unlocked when you get one of the first two pieces..

As for Nightmare Luffy, I really don't know, though I doubt that Nightmare Luffy is Playable..

And ass for Treasures, if you recieved the map pieces from their respective creatures (mud puppets, navy/agents/ robots, pacifistas, enforcers, ect, ect...) than an image of the location should be shown. If you can recognize the area, then you'll know where to go. I will give hints as to islands and a hint for each one that I know of. To get the treasures though, you need the pickaxe to unbury it.

1) Mud Puppets -island 1 -the wherever cannon can shoot you near here.. Anyone thirsty?
2) BW (Baroque Works) -Island 1 -a giant ant-lion fossil... *need a bridge to get here
3) Pirates -Island 2 -sure is a high place... Better bounce on up there! *need enhanced pickaxe
4) Zombies -Island 3 -a big gateway? Well, there's only 2 here.. Is that a lake I see..? *need Mini Merry 2
5) Navy (and agents) -Island 2 -Well, that skeletal path looks familiar.. Wasn't there land by the hiding Pandaman?
6) Evil Guardians (aka, robots on island 2) -Island 4 -not to hard to get here... Just go past a few trees and you'll find this place
7) Enforcers (Eneru/Enel's army) -Island 3 -Lakeside, but no dock? Okay! Just gotta find that path! (I think you need the enhanced vacuum for this one)
8) Combat Weapon (Pacifistas/Kuma-bots) -Island 4 -hey! This is really close to one of the boss trees! But it's surrounded by Pacifistas!
9) Gaimon (the green-haired treasure chest guy) -Island 4 -I'm pretty sure a monument's here... (probably the hardest map to get)
10) Force battles (unlimited mode only) -all islands -a battle you can't get away from? Someone might drop it here when it's over!