There's a point in Mighty Jill Off in which you have to evade four spiders for an agonizingly long time. So I think if players came away from that game remembering only one thing, the spiders would be it.
Just wanted to make sure.

Carp (Support, Dwarf Fortress)- I don't think most people would get the reference. After all, it would just look like any other fish.
Konrad (Support, Battle for Wesnoth)- Seems a bit too similar to the hologram. Plus, it defies player expectations by being killable, unlike all other support characters. And its effect is obscure.
Meatboy (Support, Meatboy)- Great suggestion! How could I forget Meatboy?
Ring(Item, Braid)- I like the suggestion, but the engine really isn't built to handle this sort of thing.
Gun(Item, Karoshi), Big Sword(Item, DROD), Axe (Item, Banana Nababa)- No weapons, please. We don't want Kovski to have a heart attack. The axe might work as a thrown item, though.
Pterodactyl(Support, Dino Run)- Good idea. We ought to try to include a Dino Run reference somewhere.
Ikaruga Shield (Item, Most Shmups)- Might be a bit obscure, and I'm not sure how well it would work.
Items from La Mulana- I have difficulty envisioning a scenario where we would have permission from GR3-Nigoro but wouldn't add Lameza.
ALSO: GARDEN GNOME (support, Garden Gnome Carnage)- Maybe. He could spin around in a circle or something.