Create a trash golem (self powered) and an un-rat (phantasm). Compare the Mana cost.
+1
You explain your plan to Esme.
"Didn't you already raise both a rat and a trash creature? Shouldn't you know how hard it is to do either already?" She asks.
"Eh, let the boy try." Bruce cuts in, "But I got a suggestion for ya. Rather than trash try this."
He tosses you one of those posable wooden dolls that artists use.
"I could tell that trash thing" He points at the still living wad of paper "was difficult. Maybe that will be easier since its more like a living thing. Oh and..." He gets up and walks to the kitchen, returning a moment later with a mousetrap, complete with dead mouse. "That too."
You start with the doll and it is indeed easier than the wad of paper, though still not as easy as the mouse you animated back at the library. It takes more energy to get the connection established and, whats more, the connection does not seem permanent. It slowly degrades. Given an hour or so it would probably be completely severed and return to a lifeless state. The mouse is another story; You animate it like you did the last time -using another nail as the core- and doing the doll and the mouse back to back really elucidates the difference. Its hard to put it down into objective measures but...you think the mouse is 4 or 5 times easier compared to the doll. Whats more, controlling it is easier. Controlling these creatures is odd to begin with; your mind doesn't quite 'fit' the body so translating your desires to it is not always perfect. With the mouse you can do just about anything other than fine motions without issue; with the doll it feels like you're heavily restricted, as though the form is fighting against your influence, rubber banding back when not constantly forced.
Once the mouse is reanimated you look around for a good phantom to dump into it. You select a small, fish-like creature that is just above your head and grab it. It wriggles in your gasp and you have to expend energy to hold and pull it down, eventually forcing it into the rat. The phantom seems to melt into the flesh of the rat and vanish, but you feel it take some extra mana from you as it does. Apparently this rat has been dead too long to retain memories and the phantom took some power from you instead.
You sit back, feeling rather tired. Its an odd, all over sensation that you can't quite focus into any specific feeling, just a general malaise.
The reanimated rat, its head flopping about on a broken neck, wanders about, much to the obvious fear of Mary and mild disgust of Esme. Bruce just stares at it, his face unreadable.