According to both ratboy3124 on our boards HERE and GameSpot (linked above) it appears Sony mistakenly released the full version of Undead Knights for PSP instead of the demo for free!Sponsored Links
Although GameSpot claims it's been pulled from the PS Store, it appears the download link is still working at the time of this writing... so leech away while you can guys! :)
To quote: "Earlier today, Sony launched the UMD-less PSP Go and added over 100 downloadable titles to the PlayStation Store. One more title could have been on that list, as a "demo" of Tecmo's Undead Knights included in the early morning update apparently included the full version of the game instead.
The 486MB download has since been pulled from the online storefront, but not before GameSpot was able to get it. The downloaded game gives no indication that it is limited in any way, with full access to all menu options, a working save function, customizable characters, and multiple playable chapters."
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