In S18E9 "Frank's Team: A Dark Day for Baseball", there are a number of corporate sponsorships in the background that are references to previous episodes. I thought it would be neat to list them all.

Baseball Sponsors

Frank's Fluids

Originally mentioned in S12E4 "Wolf Cola: A Public Relations Nightmare", this company has been brought up many times as being the peak of Frank's shell corporations. As such, this is the main sponsor for this baseball team.

Wolf Cola

Also originating in the same episode as Frank's Fluids and brought up probably just as often, Wolf Cola is mentioned in the banner at the back of the stands as the official soft drink of that baseball field.

Invigaron

Originating in S9E4 "Mac and Dennis Buy a Timeshare" and mentioned a few times since then, this is one of the brands mentioned in a banner along the fence behind the field.

Tsuma

Originating in S16E8 "Dennis Takes a Mental Health Day", I thought this was the most interesting inclusion. In that episode, Tsuma is a car brand that seems to basically be an in-universe version of Tesla (even though the Cyber Truck is eventually mentioned by name, so Tesla is clearly an actual company as well). But at the end of the episode, we find out that it was all a daydream or whatever. There is not actually a car company called Tsuma; that is just the name of Dennis's doctor. But in S18E4 "2026: A Virtual Insanity", the self-driving taxi was a Tsuma, making that the first time we saw any sort of implication that Tsuma actually is a real car company, not just a daydream named after Dennis's doctor.

Fight Milk

Originating in S8E7 "Frank's Back in Business", this brand has been mentioned several times since and has been a somewhat major part of a few plotlines.

Risk E. Rat's Pizza

Originating in S16E6 "Risk E. Rat's Pizza and Amusement Center", I don't think this company was never brought up again until this season.

Tanzerelli's Pizza Tips

To my knowledge, this business never appeared in the show before this season. Any time that I can think of that we see a pizza box close enough, it's a generic design without any specific brand logos or anything. I do see that in S18E10 "The Guys Have a Sleepover", while they were throwing eggs, a restaurant in the background had some signage with that same Italian color scheme and the words "RESTAURANT", "PIZZA", and "PIZZA BY THE TIPS". Perhaps that is a recurring background business that I have just never noticed before because they never really brought attention to it. I also have no idea what "pizza tips" even are. Searching that phrase doesn't yield any results that seem like that is a specific type of pizza product or something.

Natural Way Massage

As far as I can tell, this business was also never mentioned or anything before this season. Some massage businesses that I can think of that came up previously:

• S6E10 "Charlie Kelly: King of the Rats" Frank's gift certificates are for Ransford & Wood Day Spa
• S8E7 "Frank's Back in Business" they mention taking Dennis and Dee to a massage parlor, but make no reference to its name.
• S13E5 "The Gang Gets New Wheels" Dee goes to Fountain of Youth Spa

Let me know if I am just blanking on where this business name came from.

Memorial Parade

Similarly to these companies sponsoring the baseball team/field, most also sponsored the parade memorializing Bonnie and Sam in S18E2 "Dennis and Dee Don't Get Rich". The guardrails along the side of the parade route had a few banners that depicted that all the above companies (except for Invigaron and Fight Milk) were sponsors of the parade.

Notably, I could not get a clear enough shot of the Risk E. Rat baseball banner to tell whether it was the old "Risk E. Rat" name or if they had stuck with the plan and rebranded as "Robby-Pizza.com" as that season 16 episode had implied they were working towards. But I could find a clear enough shot of the parade banner to see that it indeed read "Risk E. Rat", implying that they must not have gone through with the rebranding, and had instead stuck with the classic name for the character/restaurant.