... and what's stopping the Cursed Pokemon from switching out?
Mimikyu does not even learn the quintessential Ghost-type move, Mean Look, so it cannot trap anything.
I think the idea is that Disguise guarantees the success of Curse (sort of like Prankster, except Mimikyu can still fire off an attack or retreat after using it, as opposed to just dying to almost anything). The opponent is now forced to either switch out or take massive damage from Curse. It's even better if you opponent tries to set up on the turn you use Curse. Not only to they lose their boosts, but Mimikyu still has its disguise.
Not sure what Red Card is helpful for, though. I think Leftovers or Sitrus Berry would be more useful, since in the case of the opponent setting up on your Curse, you'll be able to use Curse again and still live (or you could just have an odd number of hit points). If you wanted to go all-out and focus a set around Curse, here's what I came up with:
Mimikyu @ Ghostium Z
Ability: Disguise
EVs: Split between HP, Attack, and Speed. The only requirement is that the HP EV is a multiple of 8.
Adamant or Jolly Nature
- Curse
- Shadow Sneak
- Play Rough
- Shadow Claw / Thunder Wave / Toxic / Will-O-Wisp
This focuses on using Curse to force a switch. Curse can be used used twice without fainting, and if after two Curses you still have your disguise (for example, you Curse when they set up, then Curse again on the switch), you can use Z-Curse to fully heal and use Curse at most three more times. Shadow Sneak is to revenge kill mons in order to preserve your disguise for the guaranteed Curse. Play Rough is also primarily for revenge killing, but you have to be faster than the opponent. Both attacks can also be used when at low HP if you don't want to kill yourself with Curse. The last slot is pretty flexible. Shadow Claw is for stronger Ghost STAB, Thunder Wave and Will-O-Wisp cripple switch ins, and Toxic racks up damage even faster when stacked with Curse.
On the other hand, while Mimikyu doesn't learn Mean Look, it does learn Infestation, while is arguable even better.
Mimikyu @ Leftovers / Sitrus Berry / Confuse Berry
Ability: Disguise
EVs: Something defensive and/or fast
Either a fast or defensive nature
- Curse
- Infestation
- Pain Split / Substitute / Protect / Rest / Leech Life
- Thunder Wave / Toxic / Will-O-Wisp
Curse and Infestation are obvious. Pain Split and Rest both provide additional healing, but Pain Split adds extra damage on the foe, while Rest heals more. Protect and Substitute stall out the Curse damage. Thunder Wave lowers the opponent's speed and adds a chance for your opponent to do nothing, making it easier to stall with Substitute or Rest. Toxic racks up damage alongside Curse. Will-O-Wisp makes it easier to stall out physical attackers, but Thunder Wave is probably preferred.