You can grab in-game values like damage, velocity, and other entity data using the NBT placeholders. The client-side placeholder nbt_data_get can read any NBT tag that’s visible to the client (so you can get things like Velocity, Health, Motion, etc.) and you can use the server-side variant (nbt_data_get_server) if you need authoritative values while connected to a server that also runs FancyMenu.
If you’re looking for more conventional stats (player speed, health, etc.) some of those already exist as built-in placeholders (e.g., player_x_coordinate, current_player_health, etc.) — check the Placeholders page for the full list.
If you need even more advanced data that neither placeholder covers, you’d have to pull it from another mod (e.g., one that exposes attributes via commands or an API) and then feed it into FancyMenu via variables or a custom placeholder setup.