6.88d2

Since you didn't specify the hero or item, here is the interpretation of the "proper feature" for the version itself, followed by the most common context (Lina).

The 6.88d2 version represents a peak in the evolution of Dota custom games. It transitioned from a simple Warcraft III mod into a sophisticated multi-wave tower-defense and hero-upgrade experience. It has maintained an enormous following because it offers a "sandbox" feel that official Dota 2 match-making lacks, providing a space for "broken" yet fun gameplay within a balanced framework. 6.88d2

The suffix signifies the second minor revision of 6.88. This patch fixed several engine-level exploits: Since you didn't specify the hero or item,

Lina (The Slayer) Proper Feature: Fiery Soul Attack Speed Stacking. It has maintained an enormous following because it

If you meant a specific hero or item not listed here, please clarify!

It looks like you are referring to (the original Warcraft III mod) patch 6.88d2 . This was a minor, yet highly refined, balance patch released during the long 6.88 era—right before the major shift to 7.00 (The New Journey).