[daSn0wie]

IANAL, but I would trust your gut instinct on this - don't sign anything unless you're comfortable with the terms. It leaves the project in a weird state, but if your co-creator is being this aggressive to dismiss your claim, you may want to leave it this way.

Several years ago I had a problem similar in nature. A co-founder of my old-company parted with us on unfriendly terms. However, before we parted she didn't sign any paperwork. When we got accepted into an incubator and she found out, she threatened to sue us for 33 1/3% of the company. Our legal representation at the time told us that it would be considered an equal partnership if we didn't have paperwork stating otherwise. Ultimately she had all the leverage b/c she didn't sign anything.