Here's how I would handle a new Yoshi game:
- Cut out (no pun intended) the arts and crafts look. I'd personally go for something more Disney or Ghibli-esque.
- Bring back tough-but-fair difficulty - I'm not worried about isolating the kid audience, have you seen how much kids go crazy for Cuphead? This would also include giving mellow mode the axe, though wings could come back as a power up.
- Expand Yoshi's base moveset beyond just the YI moveset, albeit only slightly. His headbutt fair from Smash could work quite well I feel.
- Give the vehicle forms a little more prominence, but make it so any obstacle you can overcome while morphmated you can also tackle in dinosaur form, even if it's a little trickier.
- Bring back the Mario 2 and Yoshi's Story casts and have them coexist with the existing Yoshi's Island cast - maybe even have Wart as the villain instead of Kamek. The Story characters would require major redesigns however, given they're very tacky design-wise.
- Bring back the Yoshi rescuing system from Woolly World and having multiple babies like in DS. I'd love to add Baby Daisy and Baby Waluigi in some form
- Try to have individual stages be memorable for certain non-aesthetic aspects, such as a surplus of a rare enemy or a one-stage-only gimmick.
- Reduce the amount of backtracking, especially in castle levels.
- Ditch the flutter jump. It can still be animated as Yoshi flapping his legs, but make him more nimble and easy to control when double-jumping
- Likely the most potentially controversial change here, but give players control over their eggs' aim rather than having to wait for it to line up.
