[2]: 157  A freelancer contacted Siembieda about producing a licensed role-playing game based on the Teenage Mutant Ninja Turtles comic book, so Siembieda obtained the rights, but was dissatisfied with the supplement the freelancer produced; Erick Wujcik redesigned the game in five weeks, and it was published in 1985 as Teenage Mutant Ninja Turtles & Other Strangeness.

[2]: 160  In 1992, Siembieda sued Wizards of the Coast over its first RPG book, The Primal Order; GAMA president Mike Pondsmith helped the parties reach a compromise in March 1993.

[2]: 161  He demanded that websites devoted to Rifts and Palladium be taken down, believing that they violated his intellectual property, but eventually softened his stance in 2004.

[2]: 162  Siembieda filed a lawsuit on May 7, 2010 against Trion Worlds for its MMORPG Rift: Planes of Telara, and a settlement was reached in October 2010.

Siembieda contributed art and cartography to several early Judges Guild products for the Dungeons & Dragons, RuneQuest and Traveller lines.