Probably the earliest promotional character has no official name. Known equally as "13th Character" and "Visor Guy", he was available through a mail-away offer from Cheerios cereal. He came shipped in a small white box, and was sealed in a clear bag labelled "13th Character". Aside from this bit of printing he has no official name mentioned anywhere on the box or in his packaging. It is unknown if this character was made available outside of the US.
Tumbles The Gymnast
Originally intended for release in a playset that would go unproduced, Tumbles the Gymnast was offered via the full page advertisement seen above. This was likely sent along in the Sunday coupon section of various Newspapers.
It's unknown how he was shipped, or whether he was made available outside of the US, and the figure is among the most rare of the officially released Nerfuls.
Honey Bear was originally planned to be one of the Nerfuls characters released in the second retail series of figures, and appears on the pre-production card backs for series 2. With the cancellation of that series it seems that it was decided that Kenner (who at this time had recently absorbed Parker Brothers) would offer Honey Bear as a mail-away exclusive to the European market.
The Honey Bear offer was printed right on the blister cards of European Nerfuls that were sold just before the line's demise. Honey Bear is the rarest and most sought-after Nerfuls to receive an official release.
Honey Bear, Euro card and Tumbles advertisement photos courtesy of JB (firstname.lastname@example.org)