MAKE SURE CUSTOM TEXTURES ARE ON by opening dolphin, clicking "Graphics", going to the "Advanced" tab, and checking "Load Custom Textures"

1) Rename your desired trail to this:
Normal/Armored: tex1_64x64_c1f91fa7a7c36c1f_14.png*
Green/Armored Green: tex1_64x64_ff7e2828bc2e39d8_14.png
Red/Armored Red: tex1_64x64_baa2897636ae560f_14.png*
Blue/Armored Blue: tex1_64x64_16bd646f98d1d448_14.png*
Monochrome/Armored Monochrome: tex1_64x64_81a16c05869a0d7d_14.png***
Shadow: tex1_64x64_79eeec03956d6b76_14.png
Red Shadow: tex1_64x64_64075b51128cb8fb_14.png
Green Shadow: tex1_64x64_dfe3f0dc19b72078_14.png
Blue Shadow: tex1_64x64_9ecaac223eef57a0_14.png
Z-Alt: tex1_64x64_03065ed000c31177_14.png

2) Open the P+ Folder and place this image anywhere within User\Load\Textures\RSBE01

3) You're done! :)


NOTE*: Mewtwo and Olimar share sword trails. Regular, Red, and blue Mewtwo share trails with Purple, Red, and Blue pikmin accordingly.

NOTE**: Monochrome Mewtwo's trail is shared between him, white pikmin swings, and Pikachu's up smash. Changing this will change all 3.