User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-69.140.237.23-20120224222728/@comment-70.54.115.173-20120224225031

No. Tigrex and Amatsu would have to be on the cartridge already. The 3DS did not support that sort of DLC when Monster Hunter Tri G was released: it may be possible for Monster Hunter 4.