Give Nidalee's Cougar form an Energy as a resource

Three reasons: balance, clarity and frustration (which kinda go hand in hand) .

Mana gating is important for an adversary to know when Nidalee is weak, which is kinda the case for her spears and heals, but it doesn't make sense then that by popping into cougar form (which has no cost) she gets a pounce and free damage. making it unclear when (if at all) she is weak.

Now I understand the design idea behind Nidalee, so I wouldnt put mana on her cougar form, but energy would face her with valuable choices: She can use her cougar form to hop around the map fast >> she cant immediately transition into a full-combo gank. She fails her combo, she will have to choose: spend energy on getting the kill and not being able to get out // no kill and bailing out.

For clarity it's weird her mana bar is shown, but her cougar form isnt costing any mana. I have had this happen to me a few times where I engaged her when she ws oom only to get shredded by her full cougar form combo. That's bad clarity. So another option would be to just remove the mana from her cougar form (for enemies POV).