For any of you that had trouble on Plantera, heres what I did:

Full Spectre Armour

Menacing Mana Flower

Menacing Lightning Boots

Menacing Obsidian Shield

Menacing Star Veil

Menacing Ghost Wings (Can be anywings wings, just make them menacing)

Mythical Crystal Storm

A bunch of greater mana potions

A large vertical amount of space

What i did was just go up and down shooting plantera with the crystal storm and when i stopped flying, i just fell down (dont hold up while falling) through Plantera.

If this doesnt work for you, try Shroomite & Megashark, and replace the Mana Flower with a ranger emblem.

Use Cursed or Crystal Bullets

Note:when I did this, no healing potions whatsoever were required. If you try megashark, you will need healing potions.