ｎ番煎じかもしれないけど。ほんとに個人的です。
サーナイトの耳突起は絵柄上原型でも頭からはみ出させてる方は
メガシンカの方をそれよりもっとはみださせると差別化できるかも？ご参考までに

This might be the umpteenth time someone has said this, but these are really just my personal thoughts.
If, in your art style, you already draw Gardevoir’s ear-like protrusions sticking out from the head more than in the original design, then you might be able to distinguish Mega Evolution by having them stick out even more.
Just for your reference.