The full Mrazek ride is nirvana. Long, beautiful cross-country trail in the Tumalo Creek drainage. It has a little taste of everything: logs, ramps, roots, bridges, ridges, pines, views, and plenty of trail.
Two-thirds of the way down Mrazek, there is a Black Diamond option that splits from the main trail and will meet back up in ~1 mile. It is a bobsled blast. Also, at the very end of the trail, descending to Tumalo Creek/Shevlin Park, there is a non-optional Black Diamond section of trail. It is a rocky technical section with switchbacks, but boy is it fun.