To answer the easiest question first, yes I am working on the Monster Arena.
It is currently 25% complete, with 1/3 files done.
It will also be the first part of the RPG IH that will have 100% vBised templates to work on all styles/browsers [/showoff]
As for the pow() error: Wtbf

Are you sure you didn't piss about with the query in showthread.php?
The error is derived from this line in /includes/functions_showthread.php:
PHP Code:
$level = fetch_rpg_level($post['xp'], $vboptions['rpg_exprate'], 1);
Where $post['xp'] seems to be undefined.