See, this is an example of [url=http://tvtropes.org/pmwiki/pmwiki.php/Main/GameplayAndStorySegregation]Gameplay and Story Segregation[/url], which happens to be a common thing in Magic. Elbrus requires combat damage to a "Player" and not a "Creature" because evading combat damage on a Creature is far easier than evading it as a Player. If it were combat damage to a Creature, the artifact would be considerably more difficult to transform, and would not be as playable. Even accounting for the Top-Down design of the Innistrad block, summons wouldn't transform the blade because they are just that, summons. The Shagaru Magara is an actual living thing (or as close enough that makes no difference), and therefore has blood that can be used to transform Elbrus. Furthermore, were it the case that only the blood of mages could unseal the blade, combat damage to Planeswalkers should also transform Elbrus, right? Again, due to game design, the inclusion of an uncommon permanent type was not necessary. It's all a matter of not taking things too literally, otherwise you have walls wearing pants and [url=http://img.4plebs.org/boards/tg/image/1367/59/1367591415251.jpg]Nicol Bolas beating people with Nicol Bolas[/url].