Yes, you are the first ones to actually kill the Star Spawn and have most of the party live. You really aren't supposed to win with guns, but so many impales with shotguns can blow that out of the water. (/Pun).
One other group managed to collapse the pit tunnel and only lost a couple players, but that is only a temporary fix as the Star Spawn is still down there.
One group managed to kill it in a suicide run. They went exploring the lower tunnels and got trapped in the main room below. They tried to fight it straight up, and 3 died in the first round, 2 more in the 2nd, it was a slaughter. So the last character who had a bundle of dynamite, lit them and ran at it to give him a big hug. It was wounded pretty bad already and the 5 sticks of dynamite at point blank range did it in.
There are several ways to deal with him, but you didn't really investigate any of those possibilities. I won't go into too many details, but there was a spell in town to banish him, there were a couple ways to get weapons that bypassed his massive armor. So combined with shotguns, that would work. Tommy guns don't do so well, because only the first bullet can impale, the rest are pretty useless, doing 1 or 2 points max.
I have come up with an "accidental" way to deal with him as well involving the 2 statues. Didn't really apply to you as this was added after you were in it. Sorry the module changed as you played.
You could collapse the tunnel, but you had to go down into the pit, and plant the dynamite in the walls to cause them to collapse. Dropping it from above would never work. To do this properly you probably have to send someone down to distract the Star Spawn long enough to get it planted and get back up the ropes. You could use some quick pulley rope system with counterweights, but that would involve a lot of work and engineering, but could be done.
Dynamite really won't do that much ecspecially individual sticks because of their fuses. All he has to do is get a little bit away from it, and odds are it won't even hurt him. When you heard the footsteps running away, that was him getting away from the dynamite. The best use of it, besides collapsing the tunnel, would have been to set a trap with it, using an electrical detonator with several sticks. Lure him there with lamb chops (his favorite) and set it off. The girl at the hardware store has a high demolitions skill and could rig it up for you and is willing to help.
While the Colonel bugged out when he saw the deep ones, he is an expert on military tactics and could have drawn up the plan to do it.
Phil wasn't designed to be too tough, but in every playtest he went down like a cheap whore. So I've added an NPC to the book to give him a bit of protection. A backer from Kickstarter helped design her. You never went to the Pigeon Cove chapel. If you had you would have run into Rev. Sardonicus. He maintains the chapel and is the front man, being charismatic and a slick salesman. But has no real power. Given enough interogation, he flips on Phil and the whole cult as to what's going on.
In the book, Sardonicus is married to Raven "Shadowz" Alexis. She is seriously attracted to power and will do whatever it takes to get it. She originally thought Sardonicus was the power behind the cult, when she found out she was wrong, she has started having an affair with Phil and was planning to kill Sardonicus. She has a couple spells to manipulate shadows she can use to make him harder to hit and gives him a chance to escape if he gets hurt but not killed.
Phil is actually a pretty powerful wizard, but is using all his magic to keep the artists coming to town as sacrifices and to keep the Star Spawn pacified and not running rampant. He only has enough magic to call his spirit animal (the crow) to spy on you or attack you.
There is so much to do an see in the town, you only hit maybe 20% of it. But spread out over 2 years its hard to remember everything. So many back stories you just barely touched on or didn't follow up on. The chapel, the witch house, the cage behind the hardware store, the names on the list you found. I know you found the tunnels and went for the win, which was the right move. But I like my worlds to have a bit of depth to them.
I am changing up a few things. Getting rid of the illusions from the first scene, nice idea but can be so abused. So instead of the flat and the 2 boys turning into cyclops, your cars are attacked by a swirling mass of crows, which can cause you to wreck your cars. It works much cleaner and fits with the crows watching you all the time.
A bunch of names are changing due to a special backer level to allow people to pay to have their name be an NPC. So Phil is actually changing to Gabriel in the book. I actually like it better. I am so use to calling him Phil it seems strange, but Gabriel I think is a better evil NPC name.
I am providing the players with a map of the city. I should have done that from the beginning. Not sure what I was doing with the whole, no maps, it just makes things harder to understand. In the book, there will be a Keeper map with all the important info on it. And then a player map with only a few buildings marked. The Woods House, the Police station, the Library, Railroad station, and the Post office/telegraph office. that will be perforated so the Keeper can remove it and give it to the players. It's really nice.
Any other questions.