An idea for eternatus:
Since etenatus did originally come from space she and Deoxys (if collected) could have a scene where talk as freinds and working together on the MC.
For the eternatus character a uniqe idea for her image is at first show her with a flat chest but tall. The MC would need to stimulate her enough for her breast to pop out at the end of battle or when the sword and shield energy's combine in her at end of battle and would be her week point like lugia is to anal since she was pyschic type and weak to surprise attacks. Since etenatus is a chaotic kind of type their weakness could be their breasts. Since she is from space and can change her form her breasts being hidden could work for her since she never had anyone be able to get close to her and give here stimulation and they could be told they are size that the MC could sleep on entirely since she is 66 FT tall and that's without being pregnant yet. Her color should have a purple tint to her since in sword it was red and in shield was blue so both together be purple. This idea is for gen 8 so there is a lot of time for better ideas to come out.