As far as Ed was aware, there was no method to fight a giant blood beast in his mind. Maybe if he recovered his memories but as of right now most definitely no. Considering the fact that the gauntlet more or less acted as a core, the closest comparison would be a golem.
'You go for a golem's core usually' That was already what he instructed Var Agus to do so the question was therefore how exactly did one go for the golem's core?
Logically speaking, as long as the beast could control that much blood it was near impossible to go near it, no?
Eliminating close combat it left only ranged attacks as a viable strategy. The problem was that spears and arrows or any other rudimentary weapon of that sort would just bounce back or prove entirely ineffective. Thus, the most obvious method to attack the beast would be with magic.
