How to simulate an Open Drain Output (for I2C) in LTSpice?
Well, you have one very serious problem shown in your images. You have specified the pulse period to be \$10\:\mu \textrm{s}\$, but the on-time to be \$500\:\mu \textrm{s}\$. That's not going to fly, no matter how you do the rest.

But then you have another serious problem. I assume you want to see an RC time constant taking place. But you've wired up your \$3.3\:\textrm{V}\$ source directly across \$C_1\$. So, once again this isn't going to fly.

It is only a minor problem that you probably don't have much information on your open-drain NMOS output's characteristics. Effectively, you can do reasonable work just knowing the approximate equivalent \$R_{on}\$.

So, I'm going to read between all the lines and take a clue from your circuit about how you want to simulate the switching process. LTspice just happens to have a "SW" part you can probably use. It supports three modes: ON/OFF mode, ON/OFF with hysteresis mode, and a gradual ON, gradual OFF mode. Use the help and type in SW and select that and read the documentation on it. You should be able to achieve what you want in approximating an open-drain output with the SW part (which can be selected easily using F2 to get the dialog box with parts in it.) Since you were looking at an RC time constant of about \$100\:\mu \textrm{s}\$

Here's what an example circuit might look like:



I've adjusted the period to exaggerate the curves a bit. There are about 5 tau's of time allowed for \$R_1\$ to charge \$C_1\$ back up, so it gets almost back to the top there. Also, note that I set \$R_{on}\$ on the switch to \$100\:\Omega\$. You can set it where you want. But this is one approach.

(By playing with the \$V_h\$ parameter of the switch model, making it negative, you can even get a rise-time out of the switch. I've set it to 0, which just means ON/OFF behavior.)

EDIT: Here's the complete deal from my example: