Common Candy: Decreases your Pokemon's level by 1.
Yes.... Except...
Sweet Candy: Decreases your Pokemon's level by one. Increases friendship by a great amount.
Bitter Candy: Increases your Pokemon's level by one. Decreases friendship by a great amount.
Replacing Rare Candy altogether...
GF seriously already PLEASE do this...
Clipper: Replaces need for HM Cut.
Icarus Wings: Replaces need for HM Fly.
Surf Board: Replaces need for HM Surf. (Make Surf a TM or level up move instead so no fans cry about it... <.<)
Power Gloves: Replaces need for HM Strength. (Same as Surf)
Paper Fan: Replaces need for HM Defog.
???: Replaces need for HM Whirlpool.
Drill: Replaces need for HM Rock Smash.
Grapple Hook: Replaces need for HM Waterfall and HM Rock Climb.
They could also replace some HM requirements altogether and make different ones... But with items as well...