Also airing Friday, May 8, 2015: “Hawaii Five-0,” 9 p.m. on CBS and “America’s Ballroom Challenge” on KCTS.

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‘Mysteries at the National Parks’

According to the Travel channel, not only are there mysteries in castles and museums, but now you can find them at National Parks (!). Tonight’s back-to-back episodes look for the elusive Chupacabra in Puerto Rico’s El Yunque National Forest, and unexplained disappearances in California’s Shasta National Forest. 10 p.m. Friday, May 8, on the Travel channel.

Doug Knoop: or on Twitter @dougknoop

Also on Friday

“MLB Baseball,” 7 p.m. (ROOT): Oakland Athletics at Seattle Mariners (Live).

“Shark Tank,” 8 p.m. (ABC): A synthetic human cadaver for medical testing; personalized superhero action figures; sunscreen misting device; Squatty Potty update.

“Grimm,” 8 p.m. (NBC): As Hank and Nick get close to identifying a vicious serial killer, Wu’s life is put into jeopardy; Juliette forms a new alliance as she pursues revenge; Trubel returns to Portland.

“Hawaii Five-0,” 9 p.m. (CBS): After apprehending a fugitive, a bounty hunter is murdered; Rachel reveals a secret to Danny that has ramifications; Chin talks to McGarrett about his concerns regarding Adam; a fanatical patriot wants a new war on terror.

“Lost Girl,” 10 p.m. (Syfy): Bo and Tamsin disagree when a young Fae asks for their help; Trick has a mysterious case for Dyson.

“America’s Ballroom Challenge,” 10:30 p.m. (KCTS): The winning couples in the four divisions compete across dance styles; performances from the Cabaret division and Pro-Am division.