One unfortunateActor Allusion is possible in the game All-Pro Football 2K8. It is possible to assign O.J. Simpson to a team called "The Assassins," where the game randomly has him do a throat-slash taunt and a large stadium robot make stabbing motions when he scores a touchdown. Oops.
One of the many, many throwaway gag lines in The Dig occurs when you ask one character about another, who has managed to disappear on you. "Have you seen this boy?" In pitch-perfect T-1000 inflection. Robert Patrick voiced the main character, Boston Low.
A bizarre example using sound effects occurred in overlooked Game Freak gem Drill Dozer. The game used many sound effects from the remakes of the original Pokémon Red and Blue games, which were made by the same company. For example, the sound effect for repairing the eponymous machine mid-level is the same as when one uses a Potion on a Pokémon in FireRed and LeafGreen. After beating the game, one could enter a code to make an aesthetic change to the game, such as the outfit of the protagonist Jill on the "Garage" menu, one of these outfits being that of the female protagonist from FireRed and LeafGreen.
When Gilliam Yeager in Original Generation runs into Masaki Andou, Masaki asks him if they've met before. Gilliam looks terrified for a moment before brushing it off with "Nope." Masaki had fought Gilliam in the Alternate Continuity that Gilliam came from, the game Hero Senki, which Gilliam was the endboss for.
Also, there's references in several of the games to the appearance and/or voices of the various characters... some of which are voiced by the same voice actors ("You know, you look and sound a lot like..."), have the same character designer, or are voiced by two seiyuu who have voiced other famous roles. For example, in the Alpha series, Mobile Suit Gundam hero Amuro Ray flirts openly with Misato from Neon Genesis Evangelion: Two of their previous roles were Mamoru Chiba/Prince Endymion and Sailor Moon.
Richard Krueger calls Joey Jones "Jojo" at one point. Besides referencing Joey's name, Richard is voiced by Jurota Kosugi, who also voiced Jotaro "JoJo" Kujo in the popular Star Crusaders OVA. In another Shout Out to Jo Jos Bizarre Adventure (specifically Jonathan Joestar from the "Phantom Blood" arc), during Scenario 14 of the American Route, Richard says "Guten morning, Mushu Daijuuji. And Joestar" and "It's like a reunion joke, isn't that right, Jonathan?"
Agnes Berge is voiced by Chihiro Suzuki. When attacking with the Riot B's Proton Saber (Maximum Output), the machine takes a combat stance similar to Luke von Fabre, during one of his hidden Secret Artes. Additionally, Agnes sounds just like Luke during the earlier parts of the game, then deepens his voice significantly in later scenarios, making him sound more like Asch.
In Scenario 15 of the America Route, Soushi will state "With movement like a pendulum, barrage of accurate strikes...That technique just now, almost like boxing!", a reference to Ippo Makunouchi. Both characters are voiced Kohei Kiyasu.
In Scenario 16 of the Japan Route, Joe Maya will exclaim that "he has no name to give to fiends", a reference to Rom Stol. Joe and Rom are voiced by Kazuhiko Inoue.
At one point in UX, Lunamaria Hawke says "That's right: things go like this. When you yourself want it to be this way from how your heart feels when the natural time comes, you follow those feelings." These are the words Maaya Sakamoto, who voices Lunamaria, commented on during her wedding.
Reny, voiced by Noriko Hidaka, will exclaim in a save-quit dialogue "Sky Demon clad in flame is undefeatable!", which is what Noriko Takaya says in her home series. Furthermore, "I decline Space Monsters!" is a reference to the "Uchuu Kaiyuu" ("Space Terrible Monster Crowd") of Gunbuster.
In the ending, Johnny's quote "According to Monthly Men's Hobbies... Essayist and modeler jobs are being done recently." is a reference to Haruna Ikezawa and her hobbies, which includes writing for multiple magazine serializations. Interestingly, being a hardcore modeler became a topic in the Hobby Japan magazine.
Aoi punches Augustus with Absolute Nova Beast for a finish, like she punched Moon Will in the Dancouga Nova anime. Moon Will and Augustus are voiced by Norio Wakamoto. Doubles as Mythology Gag of characters voiced by Norio Wakamoto being punched to defeat.
Mileina says she loves Tieria, which was in the movie itself too. In Shinkyoku Soukai Polyphonica Corti and Phoron were suspected to be lovers; Mileina and Corti are voiced by Haruka Tomatsu and Tieria and Phoron by Hiroshi Kamiya.
Graham expresses desire to embrace crossdressing Alto. They're both voiced by Yuuichi Nakamura.
Both Graham and Moritsugu are non-main character Ace pilots. Voiced by Yuuichi Nakamura too.
In The King of Fighters 2002, K9999 & Kusanagi have a special intro where K9999 yells "KUSANAGIIIIII!" and Kusanagi responds "That's Mr. Kusanagi to you!". K9999's VA voiced Tetsuo Shima in AKIRA, and Kusanagi's VA voiced Kaneda.
K9999 was practically an Expy of Tetsuo anyway. So much so, in fact, that he's not going to be used in the series again.
Lego Star Wars: The Complete Saga has this in reverse, with Indy unlockable, for the same reason - as well as to promote his game, as you can only unlock him after watching the trailer for it in the Hub Level.
In Super Smash Bros. Brawl, best friends Snake and Otacon cheer 'Falcon PUNCH!' and 'Falcon KICK!' while fanboying mutually over Captain Falcon. The joke is that Captain Falcon was voiced by Otacon's Japanese voice actor in the non-canon anime. Snake also comments that Sonic just gives him a bad feeling, which is a reference to Big Boss having the same Japanese VA as Eggman (in the English version it comes of as either a non-sequitor, a Take That to Sonic or a reference to hedgehogs eating snakes in real life).
The MSX2 version of Metal Gear 2: Solid Snake featured character portraits based on the likenesses of popular actors and celebrities.note The later ports used new character portraits. Big Boss in particular was modeled after Sean Connery. This is what inspired Hideo Kojima to, when planning Metal Gear Solid 3: Snake Eater (a game about Big Boss' younger days), make the story a shameless classic-James Bond homage.
Also, in Metal Gear Solid 3, Para-Medic's response to Snake saying he has no name is to tell him "You're a regular Captain Nemo". One of Akio Otsuka's most popular roles was Captain Nemo in Nadia: The Secret of Blue Water.
In the Japanese version of Metal Gear Solid 4, Ed and Jonathan were voiced by Shozo Iizuka and Hideyuki Tanaka (also the voice of Otacon) respectively. Both actors also played Ed Brown and Jonathan Ingram in Policenauts.
From an outtake from Wing Commander III: "Isn't that the guy from Star Wars?" Readers can make their own connection, knowing that Hamill starred in WC3.
In Tales of Graces, the main character Asbel Lhant not only looks like Suzaku from Code Geass, but also retains his gravity defying spinning kicks. They are both voiced by Takahiro Sakurai.
Further implemented by giving a Suzaku costume to Asbel as DLC. Another example is that Takahiro also voiced Haseo from .hack//GU. Malik was voiced by Ovan's voice actor as well. Hence, they both not only get DLC (and I mean, each other! Haseo and Ovan get Asbel and Malik's costumes as well in .hack//LINK), but there is a victory quote where they say lines similar to what Ovan and Haseo would have said.
The Tales series in general seems to love this trope. In the PS3 version of Tales of Vesperia, Karol, who is voiced by Kumiko Watanabe, has a Keroro costume, and even talks like him after putting it on. Taking this further, Patty, who is voiced by Chiwa Saito, slips into her Natsumi Hinata voice after battle if they're both in the party—in one case, she calls Karol a "stupid frog", then wonders where that came from.
King's Quest VI, being what it is, has Prince Alexander meet the Beast (as in, from the Beauty and the Beast fairytale). Reaching his sanctuary placed Alexander under a curse, causing him to transform into a Beast himself if he doesn't find the Beast a bride in time. Robby Benson, who voices Prince Alexander, also voiced that other Beast one year earlier.
A GameFAQs meme of responding to topics (mostly ones that question some of the design choices in the game) with "Sakurai:(Laughs)" (a response given in an interview to dodge a question) gained a spin off "Dedede: (Laughs)" after the official Super Smash Bros. website mentioned Sakurai voices King Dedede in Brawl.
In Fallout: New Vegas DLC Old World Blues, Dr. 0 (voiced by James Urbaniak) is essentially Dr. Venture as a floating brain. He even has a massive inferiority complex towards an arrogant but much more accomplished genius (in this case, the game's resident Magnificent Bastard Robert House). And, if you have the Wild Wasteland trait, you can sometimes hear him asking the Lobotomites to wash the walking eye, a reference to a device from The Venture Bros Season 2.
In the first Simon the Sorcerer game, the title character was voiced by Chris Barrie. One scene involved Simon being yelled at by a dwarf in a red shirt, who told him to "smegging well naff off".
The second installment went so far as to have Simon quote several of Rimmer's actual lines from the show, even though Barrie was no longer voicing Simon.
Halo 3: ODST is based around this trope: out of the six main characters, three of them are former Firefly alumni, and Bungie refused to let gamers forget it. The most notable is Gunnery Sergeant Eddie Buck, played by Nathan Fillion. Not only is his personality a carbon copy of Mal's, Buck's face was also modelled after Fillion's. Tricia Helfer is also onboard as ONI Captain Veronica Dare—Buck's ex-girlfriend. Helfer is Fillion's ex-girlfriend in real life too. It's still an excellent game.
In fact, the Firefly cast had previously been in Halo 3 as unnamed infantry (at the end of one Halo 3 mission, a marine voiced by Fillon will say: "Looks like we got here in the nick of time! What does that make us?). So it's kind of a loop-de-loop of references, but Bungie certainly took advantage and gave us all a reason to care about ODST in the fist place.
There's also the Red vs. Blue actor cameos in the Crow's Nest level of Halo 3 (the "Password-Lacking Marine"). In all cases, they're more or less in character for Red vs. Blue.
Mass Effect 2 features the voice of Tricia Helfer as the Artificial Intelligence aboard the player's ship, in a universe where self-aware machines have been banned for trying to destroy humanity. The allusion is wonderfully climaxed with the gently delivered line "I enjoy the sight of humans on their knees."
There's also Michael Beattie, who plays Mordin. At one point, Mordin reveals he was in a Gilbert and Sullivan production ("Always had me do the patter songs.") and proceeds to break out in song. Beattie was part of the chorus in a television adaptation of The Pirates of Penzance.
In Lair of the Shadow Broker, Liara and Shepard are outside on a ship during a storm and lightning is useful element during that segment. The lightning may be a visual reference to Lightning Farron, the protagonist of Final Fantasy XIII who shares Liara's voice actress, Ali Hillis. They go to rescue Liara's friend, Feron, whose name is pronounced exactly like Lightning's last name.
Then, in Mass Effect 3 you can come across an outpost of Cerberus scientists led by Dr. Brynn Cole, voiced by Jo Wyatt, aka Female Hawke. She calls herself and her fellow scientists "refugees," and when questioned by Shepard, she says "our stories are different, but the themes are the same." As an added gag, Nicholas Boutlon, the actor who plays Male Hawke, voices another scientist at the station.