Blissey Damage Calcs:
>252 Atk Aerilate Mega Salamence Return vs. 252 HP / 128 Def Blissey: 630-742 (88.2 - 103.9%) -- 25% chance to OHKO
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>252 Atk Aerilate Mega Salamence Return vs. 252 HP / 252 Def Blissey: 466-550 (65.2 - 77%) -- guaranteed 2HKO
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>252 Atk Lopunny High Jump Kick vs. 252 HP / 252 Def Blissey: 394-464 (55.1 - 64.9%) -- guaranteed 2HKO
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>252 Atk Lopunny High Jump Kick vs. 252 HP / 128 Def Blissey: 532-626 (74.5 - 87.6%) -- guaranteed 2HKO
And here's Chansey (w/ Eviolite)
>252 Atk Aerilate Mega Salamence Return vs. 128 HP / 252+ Def Eviolite Chansey: 313-369 (46.5 - 54.8%) -- 64.5% chance to 2HKO
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>252 Atk Aerilate Mega Salamence Return vs. 252 HP / 128+ Def Eviolite Chansey: 438-516 (62.2 - 73.2%) -- guaranteed 2HKO
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>252 Atk Lopunny High Jump Kick vs. 252 HP / 128+ Def Eviolite Chansey: 368-434 (52.2 - 61.6%) -- guaranteed 2HKO
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>252 Atk Lopunny High Jump Kick vs. 128 HP / 252+ Def Eviolite Chansey: 262-310 (38.9 - 46%) -- guaranteed 3HKO
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>252 Atk Lopunny High Jump Kick vs. 252 HP / 252+ Def Eviolite Chansey: 262-310 (37.2 - 44%) -- guaranteed 3HKO
Final things I would like to conclude with:
- Ditch Blissey. Eviolite Chansey all the way.
- 252 Defense/ 252 Special Defence/ 4 HP is a very good idea.
- 128 Defense does not work.
- Your HP, to be honest does not change things all that much, so put more into Defences. Plus you have Wish support, so that's going for you.