Well. Gen a new world, crack open its temple, murder its golem until it drops a picksaw, then go back to your original world and dig your way in. Easy peasy.
May not be necessarily quite so "easy peasy", considering how irritating drops can be at times. I had to kill the golem 25 times before it dropped the last of its 1-in-8 drops.
Plantera at least I can understand, since apparently the Axe has a smaller chance of spawning than any of the other items for some reason.
Head to hardmode underground jungle, find chlorophyte, fail to mine it, discover that I need hallowed equipment to mine it.
Get annoyed at the fact I'm never going to get it barring cheats because I cannot beat HM bosses and have nobody to play with, barring the server which I said I'm leaving and I'm sticking to my promises dammit!
Also, the server lags a fair bit for me, anyways. Something you can do without when you have a boss that can kill you in a few shots.
Why can't you take on the hardmode bosses? They're tough the first time around, sure, but with potion buffs and decent-tier equipment they're perfectly doable. At least, the Destroyer is.
Make sure you've got a set of wings and adamantite/titanium (actually, orichalcum may even be better for taking him out because of its set bonus, if you have it) armor, set up an arena (doesn't need to be that fancy, just a wooden platform up above the ground a bit), buff up and go for it. If you have Crimson in your world, get enough ichor and souls of night to make a golden shower spellbook, as that works wonders against him. If you're lucky and have a decent snow biome, you can try going after ice golems until you have the even better frost armor set, which works wonders against worm-types because of its set bonus (and I believe it has higher armor than adam/titan armor). Ice golems can be a bit of a pain though if you don't already have good equipment, but you can easily lay traps for them (They're big and they can't really jump).
The wiki has a number of strategies and guides based around taking on all the hardmode bosses, Destroyer included. Some of them are outdated or haven't been taken into consideration yet after the new version, but a few others hold true. But really, potions. Potions will get you through a lot.