Ideas:

• The true Eye of Cthulhu's entry would be unlocked at the same time as Moon Lord's (unless you kill it by itself somehow)

• The Pirate's Curse would be connected to the Pirate Captain banner(that is, they share the banner and are affected the same way.)

• The jungle mimic and golden slime banner would only require 25 kills opposed to the usual 50 (because they're rare)

• The Plantera's Tentacle entry would be unlocked the same way the Hungry's entry is unlocked.