1- Mirrorblade
Once per combat you may, instead of rolling a d20, use the value of a d20 one of your opponents just rolled. You must declare this when they make the roll you want to mirror, and it must be used to do approximately the same action (attack for an attack roll, trip if they tried to trip someone, etc)
2- Chainsword
3d8, doubles deal double damage, triples deal triple. If you hit with this, you can't make any more attacks this turn.
3- Tent-Spear
1d10 piercing and force damage. When thrust into the ground (can be done as a reaction), creates a bubble of force. It has 20 hp and all attacks against it hit. If the hit points are reduced to zero, the spear is nonmagic for the purposes of attacking until the next dawn.
4- Kinetic Armour
Absorbs 5 damage from an attack, up to 25 damage total. The stored energy can be released as extra damage on a melee attack, or all 25 damage points can be released in a 10-ft nova around you Dex save for half).
Metal sphere on a long cord. Changes weight, size, & length to maximize impact of it's swing. Targets within 10 ft take 1d10 damage, within 20 ft take 2d10, and within 30 ft (max range) take 3d10, but at a -2 to hit because they have more time to dodge.
6- Conceptual Sword
Looks like the minecraft sword, or what you picture in your mind when you think of a sword. Deals 1d8 psychic damage in addition to regular sword damage. Can be 'stored' in the wielders mind, in which case it appears as a tiny sword-cross-like tattoo on the temple. If it leaves your hand you can re-summon by imagining, so it can be thrown but not perfectly (it's a conceptual sword, not a conceptual throwing axe or whatever), so attack at -2. Needless to say it can deal damage to ghosts, demons, faeries, illusions, etc- anything that's 'conceptual' or 'imaginary' in nature.
7- Mathematical Blade
Angular blade covered in numbers, squiggly formulas. Looks a bit like a very long right-angle triangle, complete with trigonometry markings. Could be found as a anything from a dagger to a greatsword. As you fight (has to be an actual fight), collect numbers rolled in combat (from damage or low d20s) until you have a full set (1-4 for a dagger, 1-12 for a greatsword, etc). A full set can be turned in for an auto hit with the blade (declare before you roll), or to turn a hit with the blade into max damage (can be used on critical hits for truly stupendous results.)
8- Ancestor Sword
Forged in a fire kindled from the bones of a revered ancestor, or a bear or something strong and awesome if an appropriate ancestor is unavailable. You have advantage to Strength checks and saves, and on Wisdom saves, while the sword is in your hand. The sword also deals damage to ghosts and spirits- it's actually two swords, one real and one ghostly, so enemies who can be struck by both (like many demons/devils, liches, slaad, etc) take both damages.
9- Mace of Many Metals
Studded with adamantine, silver, cold iron, oak, etc etc. Deals 1d8+str damage, and probably bypasses any and all damage resistance or immunity based on physical materials. Enchantments woven into the mace mean that it even deals 1d4+str damage to
10- Inevitable Sword
Every time you miss with this sword, you get a stacking +1 to your next attack with it, and +1d6 damage on your next hit. If you switch opponents, start over at 0- very similar opponents might count as the 'same' for these purposes.
