I occasionally get PMs asking for permission to use my music in videos and games, to which I usually don't provide a timely response since I don't actively use the site anymore. Therefore:
In addition to whatever license is listed on each audio page, all songs under my profile may be used according to the CC BY 4.0 license. This means you may use any song as you wish, for any purpose (commercial or not), and redistribute under whatever license you want. Under no circumstance do you need to ask me for permission!
For credit, just write "Buoyant" as the artist name, and include the title of the song (without the dumb ASCII art that some of my song titles have). A link to the audio page on Newgrounds is appreciated but not required.
Speaking of licenses, I would encourage everyone to avoid the "share-alike" clause when selecting a license. Forcing others to use the same licensing terms as yourself is going to cause more trouble than it's worth IMO. Personally I've removed the "non-commercial" clause as well since I think any loss of potential royalties is well worth the reduced friction.