Proto:Pikmin 2

A playable demo of Pikmin 2 is present on GameCube Interactive Multi-Game Demo Disc Version 18. The build date is a little fuzzy, though two timestamp files place it sometime in June, about two months before the US final was released. The fact that it appears on the same disc as a Paper Mario: The Thousand-Year Door demo (itself dated June 21, 2004) seems to support this.

Treasure Differences
Mostly the same, with the following differences:
 * The Master's Instrument, Decorative Goo, and Flame of Tomorrow use their original Japanese textures.
 * The Silencer is still 666 Pokos, not 670.

Other than that, they're functionally identical to the final American version.

Treasures
A few treasure names were changed in the final American version:

* Treasure acquired screen only.

Of note are the Potent Pummeler and Adults-Only Symbol, whose names were changed completely.

The Potent Pummeler was probably changed to curb the association of the Maple Leaf treasure with a pot leaf (it didn't help), though its description is identical to the final.

The Adults-Only Symbol was also changed, as was its description, likely as a result of censorship. More on that here.

Equipment Names
The Treasure Gauge is known as the Pikpik Radar in the demo text, which is what it's known as in the early English script.

Challenge Mode Names
The Snack Pit is known as the Beverage Hall in the demo script. This is more in line with the early script's name, Messhall of Libations.

Treasure Series Text
The series completion texts fit in three lines in the final. Most of them run longer in the demo text, so they were truncated...which is unfortunate, because they're more interesting in their unabridged form. Additionally, most of the treasure series names were changed (the only ones that didn't were "Space Love" and "Blast from the Past").

Gourmet Series
The ship's avarice is missing from the final text.

Paleontology Series
The Ship is well aware that it's probably ripping people off in the early text.

Cook's Arsenal Series
And now the ship knows it's ripping people off.

Modern Amenities Series
The final text is less sinister.

Industrial Set
Text rewritten to be less self-centered.

Crystallized Emotion Series
The ship's bamboozling nature was toned down in the final game.

Mystical Energy Series
Identical to the final, except for the last excised sentence.

Ancient Ad Series
The suggestion of a logo for Hocotate Freight is only present in the demo text.

Odd Logo Series
Another self-promotional idea removed.

Explorer's Friend Series
The Ship is so lonely...

Napsack
Changed to fit all the text in the message box.

Menu Text
This text is used in menus, so it's the last section.

File Select
Since "debt" wouldn't make sense once the debt's been paid, this was changed.

World Map
Same change as above.

Cave Entrance
With the way the game tracks treasures, the demo's label doesn't really make sense.

Cave Exit Prompt
Ye olde formatting.

Game Completion
Hey, it's those two changes. Again.

2-Player Mode
These two lines were corrected for space and accuracy: either a Fiery or Watery Blowhog can drop, so the first line is incorrect anyway.

Words to numerals. This is only the case with the 1P text - the 2P text is identical to the final, numbers and all.

Challenge Mode
Two sentences become one with the magic of commas.

Options
Hz is no longer squished with the number of hertz.

Further separation.

This line was completely omitted from the final game.

Memory Card Screen
Changed so people don't get confused that their Memory Card is physically damaged.

"Different Memory Card" changes to "original Memory Card" for, uh, technical reasons.

Edited for accuracy.