@TakeWalker Yeah, I think you misunderstood. Killing Aeon Master is the easy way to end the first phase, not for flipping the shield.
To kill four Aeon Men in one turn you need to have Aeon Master and Oblivaeon in different zones. At the end of Oblivaeon’s turn, he should play three Aeon Men into the other zone (the one with Aeon Master in it). Hit Aeon Master to pop a fourth one out, and then concentrate on bringing them all down to low enough HP to wipe them in one turn.
Once that’s done and the shield flips to Counteraction Aura, then you focus fire on Aeon Master, because killing him will wipe out all the Aeon Men and should remove the shield to move you into phase 2. The only way it can go wrong, really, is if one of the other scions just happens to play Aeon Assault between the last hero turn and Oblivaeon’s turn. It’s usually worth using some deck control to be sure that can’t happen, if you have it, but often you just have to trust to luck.