Along with changing the form of Ogerpon and the type of Ivy Cudgel, Ogerpon's masks give her a 20% power boost to any move of that mask's type.
However, if a Pokemon other than Ogerpon holds a mask and uses Ivy Cudgel (by Metronome, Sketch, etc.), then Ivy Cudgel's type is still Grass. The Ivy Cudgel change only works on Ogerpon.
My question is if the 20% power boost works the same way. For example, if I gave a Quaquaval the Wellspring Mask, and had it use Aqua Step, would that move be boosted?