As you can see from Toriyama’s drawing (taken from the game’s strategy guide, picture courtesy of this Japanese retrospective on DB Famicom games), Kurilien is a 4-armed alien wearing clothes identical to the Oorin Temple uniform Kuririn wore back when he first appeared. It therefore seems likely that his name comes from combining “Kuririn” with “alien” (エイリアン/eirian in Japanese). Why would Toriyama make such a creature? Was he just too lazy to come up with an original outfit? Or does he secretly have something against Kuririn? Either way, despite Toriyama’s character design, Kurilien’s Oorin Temple-style outfit isn’t really depicted in his actual game sprite.
Also, despite his title of “#1 assassin in the universe”, even the game’s official strategy guide notes that Kurilien is actually an absurdly weak enemy. Lacking the badass weapons shown in Toriyama’s picture, he only attacks by launching out two of his arms like boomerangs, and when you approach him close enough, he’ll simply stop attacking, allowing you to just keep hitting him until he dies.
Here’s a video showing Kurilien’s rather brief appearance in the game (Olivier Hague was kind enough to post this video in an old thread). He's featured in level 11. Levels 1-6 of the game cover the first 2 manga volumes, with the original search for the dragonballs. After that, levels 7-10 take place in a “Kung-Fu Tournament” (apparently different from the Tenkaichi Budoukai). Finally, levels 11-14 depict Goku borrowing the Dragon Radar from Bulma and heading out in search of his grandfather’s keepsake, the 4-Star Ball…in outer space! There, Goku encounters Toninjinka, the leader of the Rabbit Gang, who tries to exact his revenge on Goku by sending Kurilien after him. Goku defeats Kurilien as well as Toninjinka, after which he obtains a dragonball, though it turns out not to be the 4-Star Ball. Though the game came out on November 27th, 1986, when the manga was well into the Uranai Baba arc (DB chapter 100 came out 3 days earlier), for whatever reason the game makers decided not to adapt the RR Army story arc and instead made this new “Goku in Space” story*.
While Kurilien himself is easy to defeat, on the whole Mystery of Shenlong is insanely difficult. Few people are able to get past level 6, let alone all the way to level 11, and so most people who play the game never get to see Kurilien. Now, Mystery of Shenlong was of course brought over to America as Dragon Power, with all the references to the DB series removed, so I'm wondering how they handled Kurilien and the whole "Toninjinka's revenge" story in the game.
edit: Kurilien also apparently makes a second appearance during the last level of the game, Konpei Tower. He's not referred to by name at this point, but it sure looks like Kurilien. In fact, this time he looks far more like Toriyama's character design than he did the first time, with his Oorin Temple uniform now clearly depicted in the game sprite! So why didn't he look like this the first time? Who knows.
*”Goku…IN SPAA~~AACE!!!”
