Fortune Arc

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Aevium Lapras can be found in Amethyst Cave in the Depths. There will be a huge crystal barely hanging at the bottom. You will need to use certain moves that can remove the Crystal Terrain such as Earthquake, Magnitude and even Bulldoze. There should be a Natu wild encounter for you to be able to break Crystal Cave Terrain. The huge crystal should fall after that, interacting it will trigger a fight against Aevium Lapras. You will need Rock Climb to be able to get into this specific place in Amethyst Cave.

Xen Waste can be obtained in the den where you originally can get Shadow Beldum's at. While I didn't test it much, I initially filled Beldum's den with 15k Red Essence which you get from doing the Max Raid battles in Route 4. You'll have to go through the process of getting Beldum to obtain Xen waste.

I've considered suggesting Crests that are inspired by Rift/Pulse Pokemons and/or Crests for Pokemon that had Pulse/Rift Forms. I'm unable to translate some, but it was worth a try. So... Both Muks: The Pokemon gains the ability Libero. Tangrowth/Avalugg: Pokemon only takes 50% damage unless this Pokemon's HP is less than 50% Rotom: At the beginning of equipped Pokemon's battle and at every 2 turns, Hex will automatically be used that is delayed by 2 turns. Ferrothorn: Sets DEF and SDEF to 54 and ATK/SATK/SPD to 131. Galvantula: Calculates DEF and SDEF with SPD stat

Stoutland Crest: Normal-Type moves will deal super-effective damage against types that would normally resist Normal-Type (Excluding Ghost) Drifblim Crest: +15% SATK/SPD. At the start of battle, Pokemon will be burned. In addition, this Pokemon is unaffected by Burn damage and boosts SPD by 50% Delcatty Crest: Normal-type moves always deal neutral damage and deals 25% more damage Archeops Crest: Pokemon can survive up to 2 attacks that would KO this Pokemon. Or... Archeops Crest: If Pokemon is defeated, harshly lowers the enemy's ATK/SATK and cannot escape for 3 turns. Porygon-Z Crest: +20% SPD. Non-Same Type moves gain STAB while Same-Type moves do not get STAB. If applicable, Adaptability will instead boost Non-Stab moves