Ben M. Angel notes:

Mieceslaus doesn't appear to have very much research backing him.

There are two locations where I was able to find a Mieceslaus of the Heruli online:

Our Royal, Titled, Noble, and Commoner Ancestors & Cousins (over 137,000 names): An ancestry from New England, Virginia, England, Scotland, Germany, & Switzerland (as of 10/31/2010):

http://our-royal-titled-noble-and-commoner-ancestors.com/p571.htm#i17162

The Grenville Annex for Our Family Tree:

http://e-familyhistory.com/content/GRENVILLE_ANNEX.htm

Neither of these provide any sources for the assertion that a member of the Heruli tribe became a Vandal king. Indeed, it would seem a bit odd for something like this to happen, since the Heruli were a tribe subject to the Goths until the Hun invasion (source: Wikipedia page on the Heruli and its associated references), and according to educated guesses by archeologists noting the lack of contact between their original first century cultures, the Goths and the Vandals were apparently not on the friendliest of terms in their early years.

The earliest Vandal king progenitor with any sort of backing appears to be Radagaisus, which both the above non-cited secondary sources give as Miecislaus' son: he was described by Jordanes as a "Scythian" (no tribe given) who led against Rome in 406 a combined horde of proto-Germanic barbarian tribes that included the Suevians, Burgundians, and Vandals.

Primary source backing for Miecislaus would be greatly appreciated, of course.

Ben M. Angel notes:
Although it's a very nice flag of Yugoslavia in the photograph, Mieceslaus doesn't appear to have very much research backing him.

There are two locations where I was able to find a Mieceslaus of the Heruli online:

Our Royal, Titled, Noble, and Commoner Ancestors & Cousins (over 137,000 names): An ancestry from New England, Virginia, England, Scotland, Germany, & Switzerland (as of 10/31/2010):

http://our-royal-titled-noble-and-commoner-ancestors.com/p571.htm#i17162

The Grenville Annex for Our Family Tree:

http://e-familyhistory.com/content/GRENVILLE_ANNEX.htm

Neither of these provide any sources for the assertion that a member of the Heruli tribe became a Vandal king. Indeed, it would seem a bit odd for something like this to happen, since the Heruli were a tribe subject to the Goths until the Hun invasion (source: Wikipedia page on the Heruli and its associated references), and according to educated guesses by archeologists noting the lack of contact between their original first century cultures, the Goths and the Vandals were apparently not on the friendliest of terms in their early years.

The earliest Vandal king progenitor with any sort of backing appears to be Radagaisus, which both the above non-cited secondary sources give as Miecislaus' son: he was described by Jordanes as a "Scythian" (no tribe given) who led against Rome in 406 a combined horde of proto-Germanic barbarian tribes that included the Suevians, Burgundians, and Vandals.

Primary source backing for Miecislaus would be greatly appreciated, of course.

Barn:
Radagaisus of the Vandals, König der Herulii, född cirka 335, död 406-08-23