Was first thinking of another Water type thingy, but nah. Instead, here's a Steel type one.
The scenario:
You get a key handed to you, that opens up an elevator that goes down a hugh mountain. But before you can use it, a Skarmory comes swooping down and takes it from you. In order to retrieve the key, you need to climb up the mountain using Rock Climb. When you reach its nest, a battle ensues. Afterwards you get to use a shortcut that leads down to the elevator that you're now finally allowed to use.
Reaching the bottom of the mountain, there's still a little tunnel that you must walk through. It's pretty dark, but there's also a shimmering light at the end. Getting to the end of the tunnel you find the podium that holds the crystal. Approaching it suddenly the totem Pokemon appears and the battle begins.
The totem Pokemon:
It's a Steelix that knows the moves Gyro Ball, Dig, Curse and Sandstorm. Upon battle entry, its Defense and Special Defense get boosted by two stages. Furthermore, the allies it calls are Carbink who can use Reflect, Light Screens, Protect and Power Gem.
Beating the totem Pokemon grants you the Steelium Z crystal.
The strategy:
As you can see, this trial is less about power and more about strategizing and dealing with defensivly inclined opponents. Though a x2 boost in both defenses sounds scary, considering that Steelix' offense isn't all too great, it is beatable. Dig is a two turn move, allowing the player to switch in something that doesn't care about Ground type moves and Gyro Ball, while boosted by Curse's Attack boost and Speed drop, due to its Steel typing has a lot of types that resist it.
The idea behind the trial:
Steel as a type probably comes closest to shiny valuables, like gold and diamonds. The whole trial is a reference to those valuables (key that gets stolen, Z-Stone that shines through the darkness, etc.) while at the same time reflecting the durability of the Steel type.
