This is part of The Terrible Titans… Lurking Locked Away! quest.
Two down, two more to go! For our third ruins, we’ll be going somewhere cold. You want to head to the halfway point of the Snowslide Slope. Go past the dilapidated buildings where the pond and field are, then immediately turn left. If you visited Snowslide Slope earlier, during Calyrex’s quest, you can fly straight to the Watt Trader to save time.
For those of you who haven’t visited Snowslide Slope, from the Rock Peak Ruins, head back through the path you came, towards the three trees. Then turn right and go underneath the stone archway. On the other side, go up the incline that’s slightly on the left. Keep to the right and go up the slope past the strong Pokémon.
Turn around and continue following the slope up, towards higher ground. You should arrive near a pond and body of water, plus another strong Pokémon. When facing the water up ahead, turn right. Keep going to the end and the entrance to Snowslide Slope will be on the left. From here, follow the slope till you reach the area we described.
Once you’ve turned left from the ruined buildings, follow the path after the tall grass. Eventually you’ll reach a wider area, with a strong Pokémon (such as a Metagross) in the middle. Cautiously head right. Towards the end, there’s a stone archway on the left. Feel free to go through the tall grass ahead for some Throat Spray in the corner.
Past the archway, you’ll arrive in front of the ruins. Before going that way first, you may want to turn left after exiting the archway. You can find a Dusk Stone chilling at the nearby dead end. Also, check around the giant pillar just before the steps, towards the right, to obtain a TR05 Ice Beam.
Finally, inspect the door of the ruins for your clue: “Walk together with a living crystal of snow.” Is the answer crystal clear? You need to inspect the door with a Cryogonal as your first Pokémon. You can easily find Cryogonal in places where it’s snowing.
Inside, you’ll be in the Iceberg Ruins. Do the usual thing, lighting up the floor panels and checking out the statue at the back to confront the giant lurking inside.
This cool customer has sky-high Special Defense and solid Defense. You may want to focus on physical attacks to take big chunks off its HP bar, then perhaps switch over to special attacks to nibble away at its remaining HP. Since it doesn’t resist Normal moves like its rocky and steely brethren, you can comfortably use False Swipe.
For attacks, the frozen giant can use Ice Beam for reliable damage, Icy Wind to slow your Pokémon (although we can’t imagine they’d become slower than Regice) and Zap Cannon, which has 50% chance to hit, but causes paralysis. Finally, it can use Amnesia to enhance its Special Defense, if it wasn’t high enough already.
Of the trio, Regice is probably the easiest one to deal with. Fire-types are great for resisting its moves and whacking away at is solid defenses. Electric-types are worth considering, if you don’t want to risk being paralysed. But it only has 5 uses of Zap Cannon, so it’s not like your whole party will be stunned.
As with most Legendary Pokémon, the initial barrier is getting Regice to very low HP–preferably 1 HP with False Swipe (but red should be sufficient). Give it a good jolt of Thunder Wave or something to paralyse or sleep it, then unload your Ultra Balls or other favourite high end balls.