PvP Playground's weapons, items, and armor sets are all Components: individual pieces you can equip to change your stats and what you can do in-game. The real fun comes from Loadouts: collections of Components you can make yourself. Loadouts let players design their own playstyles around the Components they like, as well as their combos/interactions.

My favorite part of developing these kinds of systems is that every time I add a new Component, it enables exponentially more Loadouts, and the entire balance of the game can change around a single Component addition.

In this rendition of PvP Playground, I used NBT to store each player's Loadouts to unique storage locations named after their UUID. The biggest advantage of doing this is abstracting the IDs of each equipped Component. This also means you can change your username or log onto the world from a different computer and all your Loadouts will be intact.

• When you hold shift in Hide and Seek, an invisible leash knot is spawned beneath you. Leash knots (normally attached to fences) automatically snap to the nearest block position. The knot then spawns the fake block representing the player relative to its snapped location. This makes the fake block "snap into place" and blend in with the environment.
• Right click detection on FPS is done with 1.20's interaction entities. An interaction entity follows the player's vision around, consuming left and right click inputs from the player and then firing raycasts from their view. This allows you to fire with left click like most shooters, and aim down sights with right click (achieved by giving the player slowness to zoom in their FOV).
• The Gold Rush map is full of "cave air", a different block than regular "air". When players mine gold ore, they leave behind an air block. After the game is finished, the map repopulates all gold ore by replacing air blocks (NOT cave air) with gold ore.
• Tapping the sneak key in Ham Soccer makes the player leap forward. Minecraft doesn't allow you to modify the player's motion directly, so instead ~20 invisible slimes spawn right behind/under the player's feet. The number of collisions in that single frame propel the player forward.
• The high jumps you can perform in Geokinesis are created by applying a very high amount of the levitation effect to the player and then quickly removing it. When holding sneak to slam back down to the ground, a different levitation value is used which inverts the effect, increasing the player's gravity.
• Bedwars uses adventure mode so players can't destroy the map, but every item in the game can break every placeable/modifiable part of the map, so it seems like the game is in survival mode. All placeable blocks are destroyed at the start of each game using a stepped system where an armor stand iterates across the map and deletes all undesired blocks.
• In Witch Hunt, Track Racing, and other games where you control/own an entity or games with a voting system, player UUIDs are stored in a scoreboard and assigned to the corresponding entities to keep them synced.
• Dance of the Block and Trials both revolve around cloning (the dancefloor or the trial). To select a random entry to clone, each entry is a uniform distance apart in-game, then a random value is used with a function macro to select a random coordinate position to clone from.
• PvP Playground's Thermal Caves map has a hot and cold state. They're switched between with an invisible marker that sweeps across the map, cloning in blocks in waves and using particles to make it look like the map is freezing over or burning up. Players also hear a sweeping noise (the elytra equip sound) as the wave passes over them.
• Rather than using player selectors like @a or @p, PvP Playground treats all entities marked as "fighters" as players. This means you can have NPCs on your team or fight the training dummy in the lobby and they're treated just like any other player. While not implemented right now, this also means mobs could have loadouts and use weapon abilities too!
• The dungeon merchants in Delve are represented by armor stands at 90% scale with an invisible wandering trader on top of them. This prevents enemies in the dungeon from killing the wandering trader while still allowing you to right click for the nice wandering trader trading UI.