I think this is a (minor) bug: I didn't get the "MORE POWEER!" achievement when I got one fused power up in each zone. I needed to get two fused power ups in the 'normal' forest zone to get the achievement.
Edit: Also, not sure if this is a bug or just undocumented in the Yeeting Gym, but the downboost charge seems to be increasing (albeit slowly) when IRyS is above 150m?
Viewing post in Delivering Hope (hololive fangame) comments
Correct. "More Power" only unlocks with 2 fusions in the same zone. I just didn't specify in the description because it would be too long.
Correct. There's a slow recharge of downboost when flying above 150m. Since the player can't do anything while up there, at least this will help get the next downboost ready faster.