Potions upgrade, cauldron uses.

Potions must stack to 3 (or 7 but it need a huge amount of other improvements to be not OP.)

The ability to make potions in cauldrons! Different ingredients for different levels. For example, a leaping potion must be made with a frog leg, this will be the first level that can be made in the cauldron and improved with glowsquid sack to the second level (or frog leg is for 3 level cause they jump higher). The effect will not be so long, but the opportunity to make a potion even before going to the nether is very exciting.
The third level (you will have to re-balance effects a little for this) will be done in the brewing stand, which will be not a much stronger than the 2nd but with a longer effect time, and the 4th level with the addition of glowstone - less effect and more power. Dragon breath could be used as a level 5 access.
Then how to make cloud potion? - add a cloud! Cloud in the bottle like in the Quark mod, very useful thing.

By the way, about the the potion of leaping: the rabbit's paw should drop more often (and some special one that drops rarely... let it be with an extra toe or something.)