Okay, bear with me, readers, I'm about to get into some serious Dungeons & Dragons (D&D) lore.
We all know that Vecna is fully based on the actual evil wizard of the same name from D&D, meaning that he's a real entity that players have had to interact with many times while playing the physical game. Basically, there's a lot of history behind Vecna.
In the game, there are quite a few artifacts you can have, two of them being directly related to Vecna: the Eye and Hand of Vecna. Basically, artifacts are extremely powerful, magical properties that characters can hold during the game to give them special abilities. Now, here are how these two artifacts work:
The Eye of Vecna
Based on the information from the D&D Dungeon Master's Guide, a person who wants to use the Eye of Vecna has to (first) find the eye, and then gouge out their own eye, replacing it with Vecna's. Upon doing this, the holder can cast spells from their eye in addition to having true sight, which means that they're able to see everything as it truly is, including being able to find secret doors and use clairvoyance, among other abilities. Oh, and one little thing: if you ever remove Vecna's eye, you die.
The Hand of Vecna
Much like becoming one with the eye, to attach the Hand of Vecna, you have to remove your own hand and attach Vecna's to the stump just above your wrist. The hand allows the holder to have a massively increased amount of strength and can also be used to cast spells. And just like the eye, if the hand is removed, the holder dies.
*Now, if a person happens to hold both the eye and the hand at the same time, they become immune to all diseases and poisons and can sense when danger is afoot.
How This Applies to Season 5
When Vecna was launched out of his house and onto the ground below by Steve, Nancy, and Robin, we never got to see the state he was in—he really bolted out of there without a trace, save for the massive indentation he left on the ground below. For all we know, he lost an eye and hand in the process.
Now, do we happen to know a certain individual probably in need of a new eye or hand? Yep, our girl, Max. She would certainly benefit from these new body parts, though she would become slightly evil in the process (they are limbs from Vecna, after all). However, they might offer some pretty strong insight into the wizard himself, potentially aiding in both locating and killing him.