Mana Regeneration Potion

Mana comes back fastest when you stand still and stop casting, which is the opposite of what a boss fight asks of you. This potion removes that trade. While it is up you recover at the standing-still rate no matter how much running, hooking and flying you are doing, and the dead pause that normally follows an emptied bar is cut down hard.

That makes it a fight potion rather than an exploration one. Wearing down a mechanical boss with a mid-tier magic weapon feels completely different with it running, because you spend far less time waiting for blue before you can shoot again. Pair it with a mana flower so the drinking is automatic and you stop watching the bar at all.

Shadow chests and the pots scattered around hell both hand these out, so a hellevator run early in a world usually leaves you with a small pile before you have even set up an alchemy table.