I've been playing Spelunky for a while now, but I'm still not particularly good.
Here are some ideas I have, most of which I've done at some point.
Since I've read through the last 30 pages, they should all be original(I might have missed some, though). Not being very good, I'll leave amounts out.
Also, most of the names are rather lame.Rodeo
: Ride a rolling Boulder for X second/distance.Cloggage
: Get a boulder to come to rest so that it blocks the level exit.Fishfingers
: drop a Piranha skeleton in lava.Hot Hostage
: Use a living damsel to block X arrows(or alternatively enough to kill her.The Great Escape/ Cooler King
: free yourself from a ball and chain X times in a single run.Convent in a Hole
: fall into the bottomless pit in area 3 while holding a damsel that hasn't yet been harmed or thrown, leaving her calling for help after.(probs a bug, might not happen in the latest version...)Basejumper
: Use X parachutes in a single run.Snakes on a plane
: kill a snake while it is in mid-air.Soggy Buggies!
: drown all of the spiders sent by Kali after destroying an altar.Now I'll Never Know...
: Throw a pot into the lava after Olmec.Industrial Nutcracker
: Use Olmec to crush a skull.The Italian Job
: Stick a stickybomb to the underside of a shop, steal all the stuff and get away unscathed.Killing for Pleasure
: killing all of the shopkeepers in the black market without taking any of the gold dropped when they die.Blood Hermits
: stand X living, conscious cultists on an altar at once.Overgrown Temple
: variation of the above, but using man-eating plants.Butchery
: bloody every set of spikes in a single run.Gravity Gun
: complete a run only making kills with crates.Luggage
: Variation of the above, but using chests.Key to his heart...
: kill X spelunkers with the key as the Damsel.Burnt Offering
: put X corpses on an altar after it has been killed by lava.Burning Atlantis
: Ride Olmec into the lava.Antibodies
: Get killed by a Piranha while inside Jaws.Moby Dick
: kill Jaws using only ropes.Krinkneck
: complete a run while looking up the entire time.The sky is falling!
: Complete a run without hitting your head on the roof.Blood & Bone
: feed a single man-eating plant X things.Assassin Beetle
: kill X scarabs using a stunned vampire.Nothing to see here
: find the entrance to the black market, and then cover it with a block.Bug Bomb
: Blow up X scarabs with one frog/bomb.Bullseye vs the Green Arrow
: Empty the contents of a bow onto the ground, and then make a kill with each arrow by throwing it.Bejeweled
: Spend over X at shops, but without collecting any gold.Deep Impact
: fix X stickybombs to the bottom of Olmec at once.Inspector Gadget
: get every tool and kill with every weapon in one run.Disposable Camera
: Fire each weapon once and only once in a run.Garret Jr.
: collect X gold bars without touching the ground the are sitting on in a run.Tower of Babel
: Stack X movable blocks on top of one another.Juggler
: Throw a lit bomb X times before it explodes. Lily-pads
: kill X Piranhas by jumping on them.Jaffelopes
: Run under X yetis at once while they are in the air.I can kill you with my brain.
: kill a giant alien without weapons, explosives, enemy fire, teleportation or throwable things.Highdive
: In the final level, hit your head on the to of the level and then fall uninterrupted into the lava.Red Door Exit
: collapse X crumbling floor tiles(you know, the thin blue ones) in a run.Mountain Rescue
: free X frozen cavemen in a run.
That's all I can think of at the moment.