Summary of stanza 3 from https://owlcation.com/humanities/Ode-On-Melancholy-by-John-Keats-Analysis-and-Summary Melancholy and Beauty are one, along with joy, pleasure and delight, which can evoke religious feelings. This is the way to deal with melancholy - work with it and reap the rewards.

The Solanacea are a family of flowering plants, including tomatoes, potatoes and eggplants but also many highly toxic variants.

Proserpine was the Roman goddess of wine (known as Persephone in Greek). She was forcibly abducted by Hades (Pluto) to his underworld.

Summary of stanza 2 from https://owlcation.com/humanities/Ode-On-Melancholy-by-John-Keats-Analysis-and-Summary) Instead of going under, grasp the nettle and use the pain as inspiration - look into nature and those you love. Melancholy can be a positive thing because it shows you have a sensitive soul.

Summary of the whole stanza from https://owlcation.com/humanities/Ode-On-Melancholy-by-John-Keats-Analysis-and-Summary

Refuse death, do not contemplate taking your own life, don't poison yourself or succumb to drugs because these will make you forget, which means that you'll be giving in to these dark moods. Lethe is the river that flows in Hades, the underworld, from the ancient Greek myths. Its water makes the dead forget.

Nocturnal bird of prey who sees all.

Psyche was an extremely beautiful mortal woman, often compared to Aphrodite. Aphrodite was jealous so sent her son Eros (Cupid) to make Psyche fall in love with a vile person. But Cupid fell in love with Psyche himself. However, nobody approached Psyche for her hand. She ended up jumping off a rock spire, but Zephyrus, the Greek god of the west wind, took her to Eros' palace. She is visited by him in the dark and gets pregnant. When she finally lights a lamp to see his identity, she sees how beautiful he is. She wounds herself on his arrows, spills hot oil and wakes him up. He runs away, and she is left on a river bank. Pan finds her and sees the signs of passion on her. After all kinds of drama, they are eventually reunited and married.

Skull patterns on their thoraxes.

Poisonous, along with the wolf's-bane and nightshade already mentioned.

Roman Catholic prayer beads

Keats may be referring to Medea who murders Princess Creusa with poisoned gifts and tries to murder Theseus by giving him a poisoned cup.

Also known as aconitum or the 'queen of poisons', a genus of 250 flowering plants, blue-purple in colour. Aconitum comes from the Greek for dart or javelin, because the tips of arrows could be laced with the poison and then shot at wolves. There is some speculation that both Socrates and Alexander the Greek were killed by aconitum.

Assonance, internal rhyme, insistingly negative.

One of the five rivers of the underworld of Hades, also known as the river of unmindfulness. Everyone who drank from it experienced complete forgetfulness. The word literally means 'oblivion', and is related to the Greek for 'truth' (aletheia) which means 'unforgetfulness'. So there is some kind of connection between Lethe and concealing the truth. At the same time, if the shades in Hades didn't drink from Lethe (and thereby have their memories erased), they would never have the chance to be reincarnated.