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.