>>32786557If it evolves by trade with no other requirements, make it evolve by happiness. That way you can still evolve them whenever you want, assuming they aren't already level 100.
If it evolves by being traded while holding an item, let the player use that item to evolve it as though it was an evolution stone. This way, the player still needs to get the item before they can evolve it. You could also let them evolve by leveling up while they hold the item in question, but that'd be annoying for the 3 or 4 people who actually use Clamperl, since it sucks without the Deep Sea Tooth/Scale and having to cancel the evolution every level would get tedious.
If it evolves by being traded for a specific Pokémon, let it evolve by leveling up while the other Pokémon is in the party (like Mantyke does with Remoraid). It probably wouldn't make much sense with regards to the Karrablast/Shelmet lore (if you evolved a Karrablast like this, it would "steal" the Shelmet's armor without actually removing the armor), but who really cares about that?
