Slams in general should be primary attacks (unless you have a very good reason for making them secondary) with attack bonus of +16 and dealing 1d8+7 points of damage (and when writing damage dice for attacks you should always put a number of dice before d, even if it is "1").
You don't have to give it Improved Natural Attack feats - while creating a monster you set their natural attack damage dice, the values listed in the table in Universal Monster Rules are only the suggestion and default value. The Improved Natural Attack feats should be primarily to discern individual specimens from others of their kind.
I didn't realize either of those, and thought that if a creature had 1 primary attack, its other attacks were considered secondary. I lowered its strength mod by 1 to adjust for the increase in damage. Now to adjust feats...
Well, it being CR 8 puts it in the CR range I wanted, so thank you very much for your feedback :) If you have a game you feel that this creature would slot inside of, I'd love to hear how it goes.
I would love to hear your feedback, if any, on the flavor side of things, because I like how those came out. Basically what happened is I drew a pic of what I envisioned, and saw that it looked draconic, so I added the "how to make" part.
I'm running Iron Gods right now, and my players are about to enter the 4th book, which includes an area with a color out of space. I was wondering if a color out of space's aura will penetrate a wall that it's not in, because the aura says that it will work even if the creature is in the wall, but I don't know if that extends to the color's aura just going through the wall. This is relevant, because if the aura does go through the wall, then as long as my players are on the map, they need to make a save against the aura.
I looked at the page you suggested, and I don't think that the CR discrepancy was as wide as you think. What I did was I ticked down the natural armor by 2, took off pounce, and reduced the resistance gained from the active element. I think that the increased HP and accuracy is balanced by the fact that it deals a lot less damage on a hit than is suggested for the CR.
I'm preparing to run Iron Gods for my group, and I was reading the Rumor tables in the forward, and it looks like you guys should have an editor at least give a cursory glance to them, since you skipped some numbers on the rumor tables. Table 2 skips from 80 to 86, while table 3, for the technic league, goes from 25 to 41.
Are GMs encouraged to come up with their own rumors for these sections, if it comes up?