Seems UP to me. I'm going to make two comparisons here.
1) Damage giver. Phase recluse comparison.
---Let's say you have a 10 attack creature to generate an image of, which in itself is hard since it means using an opponent's dragon (which they may not have) or using lots of quanta of another element since aether has none.
---So, simplifying it, you generate a 5/0 attack creature every turn for 2
.
---Simplifying it more, Phase Priest = 7/2 for 6
+ 2
upkeep every turn. Phase Recluse = 7/2 for 4
.
Seems underpowered in this respect.
2) "Death-effect" creator. Fractal'd ball lightning comparison.
---Both are two card combos the first time used, one card combo the second time. (Fractal + Ball Lightning first time, just Fractal second time; Phase Priest + Creature first time, just Phase Priest second time).
---Fractaling a ball lightning usually makes 6 or so. So assuming you play 5, that's 5 deaths for a total of 8
and losing the rest, but usually you won't lose much more. So let's say 8-10
.
---To use this, to generate 5 deaths it will require 10
simply through the ability costs, not even including the play costs of the creature and creature you will image (and both are rather expensive).
---It will take at least 3 turns usually to use the ability 5 times (sometimes you'll have 2-3 priests out).
Seems underpowered in this respect too.