Orizaba (18,491') is the highest peak in Mexico and 3rd highest in North America. 

Update: Sea-to-Summit Route

The “Pico de Orizaba” is the highest peak in Mexico, standing at 5,636 meters above sea level (MASL). Located on the border between the states of Puebla and Veracruz, its summit offers extensive views across the country, including a glimpse of the Gulf of Mexico on the eastern horizon, with the largest coastal city being Veracruz, situated right along the Gulf.

Mt St Helens (8365') is unusual in that it is basically a "new" mountain since the 1980 eruption which removed 1312' feet from its height.  summitpost.org lists 3 main routes, Butte Camp, Worm Flows / Swift Glacier, and Monitor Ridge (shown on the map below).  The latter 2

Frank Lenihan posted the route:

Yushan, at 3,952m (12,965ft), is Taiwan's tallest mountain. I climbed it twice using the classic two-day route, ascending from the west, climbing from the trailhead to Paiyun Lodge on day 1, and from Paiyun Lodge to the summit and back to the trailhead on day 2. For single-day ascents, most climbers spend 10-12 hours going up and down the mountain. 

Tacaná is a 4060m volcano on the border between Mexico and Guatemala. Santiago Carsolio reports that there was a previous FKT by "a German guy" of 3h15m for the ascent, 5h00m-5h30m RT. He also said, "This challenge consist of running from the town of Chiquihuite (2050m) in the Mexican side, going to the main summit (4095m) and down in just 15 kilometers, this makes it a double Km vertical challenge and then down. Tacana is the second highest mountain of Central America.

The Elks Traverse connects all seven 14ers in the Colorado's Elk Range. The peaks are: Castle, Conundrum, Capitol, Maroon, North Maroon, Pyramid and Snowmass. More information on the Colorado 14ers is here. The challenge is trailhead to trailhead.