this is a good point, it kind of comes down to how accessories that give you immunities are often ignored in favour of more useful, damage-oriented accessories.
to counter this, you should combine more niche accessories with these new ones you've created. I'll give a few examples of existing accessories that have interesting properties, ignored simply because other accessories are superior.
View attachment 268232 Flesh Knuckles - offer +7 defense. that's it. applying this to some accessory and changing the +7 to a +6 or +5 makes them viable.
View attachment 268233 Putrid Scent - enemies are less likely to target you, 5% increased damage and crit strike chance. this is kind of neat, but would you agree that you would probably take an avenger emblem over this? apply it to another accessory and it becomes viable.
View attachment 268235 Shark Tooth Necklace - reduces enemy defense by 5. this usually corresponds to a 2-3 damage increase for the player, assuming they're attacking with a weapon that deals over half the enemy's defense in damage in the first place. this item is shockingly not used in any accessory upgrades at all.
View attachment 268236 Star Cloak - a 30-damage star falls from the sky when you take damage. this one is used in the creation of the star veil when combined with the cross necklace. in my opinion, the cross necklace is downright superior to the star veil unless you're planning on selling them, but this item has potential in other crafting recipes.
I'll give some expert mode-exclusive items now. some people may think these shouldn't be combined since they're special expert boss drop items.
I just think it's a shame that these items, well, suck. they have good potential if combined creatively with your accessories.
View attachment 268238 Brain of Confusion - enemies making contact with you are sometimes confused. wait, aren't a bunch of enemies just immune to confusion? wait, aren't you supposed to not get hit in the first place on expert mode? combine this with something else to make it more viable and fun!
View attachment 268239 Spore Sac - occasionally spawns spores that deal damage to enemies. is this not incredibly fun and unique? it's just a shame that it's not viable at this point in the game.
View attachment 268240 Shiny Stone - massively increases life regeneration if you're standing still. I will admit here that this item is viable in several situations; not to say it can't be combined with other accessories for more options.
View attachment 268241 Gravity Globe - gives you control over gravity. that is, it's a perpetual gravitation potion. I never understood why someone would want to use this at all, but maybe you can answer that for me by creatively applying it to an accessory.
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here's the thing - combining these with immunity accessories and then combining those immunity accessories into a god accessory is silly. right now your goal should be to make an immunity accessory that someone who just beat plantera would use.
this is difficult. that's why combining your immunity accessories with existing and unrelated accessories will make a player stop and think - "can I make this work? would I take off one of my counterweights for this? would I take off an emblem for this?"
of course, this is not to say the Shield of the Ancients can't exist, but it doesn't need to be made of everything. it's important to force players to pick and choose sometimes, rather than let them have an all-in-one.
let me know what you think.