Come up with an evolution for a lesser-known Pokemon that would put their line on the radar. It could be a split evolution, a la Politoed, or just a straight up 3rd stage, a la Rhyperior.

Hard mode: Don't make its stat total go over 545
Lunatic mode: Don't create a new ability for it, or give it an OP ability (Huge Power, Delta Stream, Drizzle, etc)
Dante Must Die mode: Make it balanced

I'll start

>Grumpig evolution
>Psychic/Ghost type
>Abilities: Magic Bounce and Truant

Stats:
>HP: 96 (+16)
>Attack: 45 (+0)
>Defense: 79 (+14)
>Special Attack: 90 (+0)
>Special Defense: 110 (+0)
>Speed: 115 (+35)
>Total: 535 (+65)

As for moves, it'd gain access to Quick Guard and Wide Guard. This set is obviously meant to make it a good support Pokemon for doubles. Since Grumpig already has a bunch of support moves, from Trick, to Skill Swap, to Hypnosis, and etc, it would be good to make use of its bulk and give it a bit of extra speed to be able to outspeed most other support Pokemon, while also not being completely helpless if taunted.