Elementally Charged Blade

You enchant your melee weapon for 1 round and attack with the same action, with one of the following elements: Cold, Fire, Lightning or Radiant.
Enchanted, your weapon deals an additional 1d4 of the chosen elements damage on a successful hit.

Uniquely, you can also "super charge" your weapon by catching the corresponding element for 2d10 elemental damage through the following way (super charging the weapon does not damage it, since there is magic involved):

"Super charged" Cold Blade:
You can catch the cold energy from
-being inside of a heavy snowstorm weather (naturally or magically induced) by raising your weapon, [this charges your super charged weapons current max. d10 dices fully]
-sinking your weapon into a almost frozen water body which is at least 10 feet deep,
-sinking your weapon into snow which is at least 15 feet deep,
-catching cold damage from a spell or attack (like Dragon Breath) which theoretically does exactly or more damage than a 2d10 dice.

Example:
Frostbite cantrip. At character level 5, 2d6 cold damage = max. 12 cold damage, lower than 2d10 and therefor not enough to super charge.
At character level 17, 4d6 cold damage = max. 24 cold damage, more than 2d10 and therefor covers enough damage to super charge.
Ice Knife. At spell slot level 1, after the piercing damage, it explodes for 2d6 cold damage = max. 12 cold damage, lower than 2d10 and therefor not enough to super charge.
At spell slot level 3, after the piercing damage, it explodes for 4d6 cold damage = max. 24 cold damage, more than 2d10 and therefor covers enough damage to super charge.

Keep in mind that catching the energy of spells or attacks can require you to take a "ready" action to effectively make use of an allies or enemies spell or attack! Staying damage sources, like Call Lightning for lightning damage, also apply for catching.

"Super charged" Fire Blade:
You can catch the fire energy from
-being inside of a firestorm weather (not literally standing inside a fire tornado but inside the weather condition) (naturally or magically induced) by raising your weapon, [this charges your super charged weapons current max. d10 dices fully]
-sinking your weapon into a flowing or not flowing body of lava,
-catching fire from environmental fire hazards in range of your melee weapon, which do enough fire damage to cover a 2d10 damage dice,
-catching fire damage from a spell or attack (like Dragon Breath) which theoretically does exactly or more damage than a 2d10 dice. (Check for an example of catching elemental damage the Super Charged Cold Blade section above!)

"Super charged" Lightning Blade:
You can catch the lightning energy from
-being inside of a lightningstorm weather (naturally or magically induced) by raising your weapon, [this charges your super charged weapons current max. d10 dices fully]
-environmental phenomena or mechanical constructions such as traps, a tower with electrical mechanisms (or a tesla tower), etc., in range of your melee weapon (also if your weapon is in range of getting arc-ed at when normally the character would be hit), which deal enough lightning damage to cover a 2d10 damage dice,
-catching lightning damage from a spell or attack (like Dragon Breath, if it exists, if not, then something like Animated Breath I guess?) which theoretically does exactly or more damage than a 2d10 dice. (Check for an example of catching elemental damage the Super Charged Cold Blade section above!)

"Super charged" Radiant Blade:
You can catch the radiant energy from
-being inside of a solar storm (naturally or magically induced) by raising your weapon, [this charges your super charged weapons current max. d10 dices fully]
-environmental phenomena or mechanical constructions such as traps, giant sunbeam focus magnifying glass's or laser beam emitters, etc., in range of your melee weapon, which deal enough radiant damage to cover a 2d10 damage dice,
-catching radiant damage from a spell or attack (whatever attack there is that could be an example here) which theoretically does exactly or more damage than a 2d10 dice. (Check for an example of catching elemental damage the Super Charged Cold Blade section above!)

Cantrip Upgrade. The elemental damage increases by 1d4 when you reach 5th level (2d4), 11th level (3d4) and 17th level (4d4).
The super charged 2d10 damage increases by 1d10 when you reach 5th level (3d10), 11th level (4d10) and 17th level (5d10). You may choose how strong you want to super charge. The higher the d10 damage dice, the higher the elemental damage you need to super charge it and therefor the higher the spell slot required.

Creators Note: This cantrip is inspired by the Green-Flame Blade cantrip and by that one movie where a wizard catches the Lightning with his sword on top of a mountain tower. It does 1d4 damage because it gives a little bit more damage variety for 1 cantrip slot and is not a single element focused spell like Green-Flame Blade. I also don't want it to overshadow spells like Green-Flame Blade, Spirit Shroud or Elemental Weapon by giving it a higher damage dice. And the idea with super charging the weapon is that technically, if you enchant the blade out of thin air, you should be able to use an already existing, powerful enough, elemental source! But why not make it an extra cantrip? Would you really want to use a cantrip slot for a VERY circumstantial spell that requires you to have either the right weather, an enemy that can do magic attacks or a team ready to cast a spell after your ready action? I wouldn't want to spend a slot for such a cantrip. The super charged blade damage dice starts with 2d10 because early game cantrips and spells, before character level 3, are a little bit too early and weak to unlock this feature, which I want to feel properly powerful and special enough for its current level. Its damage going up to 5d10 at level 17 means that most spells can super charge it fully with up to 7th level spell slots. If I would go from 1d20 damage dice to 4d20 would that require a spell to do at least 80 elemental damage which would be just too much and require a 9th level spell! The aquired super charged damage should feel rewarding enough for using environmental conditions like a frostbiting snow storm while being inside. And yes. You can super charge a wooden sword and technically a toothpick if you can use it as a weapon.

"YOU CAN NOT PASS!" -An old Wizard, moments before solo-ing a demon Boss in free fall