Spelunky - Unlimited

[Doolin]

Since you asked...
Toughness: Being thrown by a Yeti does no damage.
Negotiator: Get discounts on goods in shops.
Stealth: You can stay farther away from enemies without alerting them.
Acrobat: You jump higher.
Athlete: You run faster.

Wow... I love every one of them.

[hyperme]

I have new enemy ideas, if you want them.

Those Bounty Hunters that I described.  They come in different flavours, such as Gun Man (has guns), Explosives Expert (throws bombs/lays C4), Strong Man (throws you) and uh, something else.

Summoners could work as minibosses.  Just let them fire their own version of Olmecs energy balls.  These could be variations of any enemy, summoning their varients.  It also has a risk/gain factor.  Kill them quick, get the items, or wait to get up more kills.

And finally,  Vacuum Trap.  A Mantrap that pulls stuff towards it with vacuum like powers.

[Audioworm]

Since you asked...
Toughness: Being thrown by a Yeti does no damage.
Negotiator: Get discounts on goods in shops.
Stealth: You can stay farther away from enemies without alerting them.
Acrobat: You jump higher.
Athlete: You run faster.

Wow... I love every one of them.

Danke.
(FTS(For The Stupid), Danke is Thank You in German.)
(NO I AM NOT GERMAN.)

[BobbyBoe]

Lasso: you can grab items with your whip. (See Tastes like Spelunky, where you can get items with your tongue after eating  the Paste)
Careful: The mattock does not break
Strongman: You treat push blocks just like normal stones and can throw them or carry them around.
Master thief: Traps will get activated after a short delay when taking the treasure
Oompa Loompa: you are an Oompa Loompa
Master of the Rope: you can throw the rope. It will activate at the place it touches the floor, an enemy or the wall first.
Bomberman: the explosion of you bomb is like a cross of 3 squares in each direction
Hypnotizer: Can force sentient beings to fight for you (Sentient = may be sacrificed)
Master Archer: your range and damage increase
Quiver of Quantity: unlimited arrows/arrows regenerate
Hardy: shorter stun time/no stun at all?
Lucky Dick: Damsels are always (Asian?) twins and thus give you two hearts.
Nerd: You do not need sunshine and thus gain infravision. Double the distance you can see in dark levels without use of light sources.
Herbicide: Mantraps are disgusted by you and will die when trying to eat you. You do not die instantly, but lose two hearts.
Remote Control: you can make all your dropped bombs detonate instantly by pressing 'd'
Nekkid Scotsman: You are naked and grow a beard. Cavemen won't attack you unless you attack them (like the shopkeeper).
Evil Dead: You have the Necronomicon. Because of your blasphemous incantations, you gain twice as much favour by Kali.
Groovy: you have a chainsaw instead of your right arm. You can not use the whip anymore. Increased whip length increases damage of chainsaw instead. The chainsaw may be used permanently. Requires Evil Dead, can not be taken together with perks upgrading the whip
Van Helsing: less damage by Vampires. Vampires are stunned after touching you because of wonderful garlic, but still do inflict damage.
Molt: Once per level, you may shed your skin and start again at the entry. This does not change your equipment, but costs you two hearts. You will find your skin at the place you used this power. It can be sacrificed or might be used as mantrap fodder in order to stun them.
Lord of the Flies: Can use the mummie's fly attack once per level.

[Doolin]

BobbyBoe, those are all awesome! Keep em coming guys!

[DungeonPheonix]

Spelunky X implemented an experience + perk system, with perks bought at shops. In hindsight, it seemed to me a little cumbersome because perk availability was tied to shops, which were rare. Being able to buy perks at any time may be an interesting feature.

I might also recommend merging perks with specialized benefits, such as gaining immunity to throw and fall damage, things like that. In Spelunky X, I found myself only buying the perks with significant or important effects, such as poison immunity, with the smaller bonuses not appearing cost-efficient. Of course, this may be because perks were available only at shops and because there was only so much experience available, making me frugal with them.

[BobbyBoe]

Firefighter: Less damage by fire, magma will not kill you instantly
Whirling Dervish: You spin around. Your whip attacks not only the enemies in front of you, but those behind you as well.
Ghost Buster: You're afraid of no ghost! The ghost will not harm you.
I believe I can fly: You can touch the sky. Once per level, you may turn gravity upside down by pressing [button].During this time, jumping moves you downwards instead of upwards. You can change it back by pressing [button] again. Warning: you will take falling damage if the ceiling is too far away, just as if you had been jumping from a high cliff.
Bullet Time: Once per level, you may change into bullet time mode. Everything else moves slower, and you get to wear sunglasses and a coat.
Pirate: You deal double damage with the machete. There will be one on the floor at every level entrance. There is a chance of a ninja spawning at the exit, willing to hunt you down.
Teleport Control: When using the teleporter, you may choose which square in an area of 4 squares in each direction you want to move to.
Barbarian Blood: You are a mighty barbarian with a russian accent. You have trusty hamster called Boo which might be thrown at enemies. If it does not hit an enemy instantly, it will run around randomly until it hunts down its prey. Boo inflicts 1 point of damage each three seconds. If killed, you will not be able to use Boo for this (and the next) level.
Oblation: You become a really crazy priest. You can sacrifice yourself to Kali by ducking on an altar. You lose 1 heart and get two ropes, two bombs, full arrows. If you are a Barbarian, Boo will also be restored to life. You can not sacrifice yourself more than once every ten seconds.
The longest one: You have longer ropes. It will get as high as possible and only stop if it touches solid obstacles. It will  extend to the ground, as far away as it might be. This means that if you throw a rope while in the air, it will go up and down.
Snake Charmer: You can sing tunes that force snakes to obey your every command. All urns on the screen turn into snakes. Snakes will not harm you, but will harm other enemies instead.
Tinfoil Hat: The alien's psychic powers will not harm you. You are immune to the attacks of the giant alien, and their laser inflicts less damage.
Scholar: You have studied maps of these terrible tombs. If you pause the game, there will be a minimap showing the level you are traveling in. Entrace, exit, shop, idol and your position are marked, too.



New items: German spiked helmet: Wearing the spiked helmet makes you immune to dropping spiders and other attacks from above, instead inflicting damage to your attacker.
Sling: Rocks are like arrows and can be fired with the sling. You can now carry up to ten rocks. Perks regarding the bow will not work with the sling.
Torch: Gives light. Double damage against plants, mummies and vampires. Has a one in six chance of burning other enemies, too, killing them instantly.

[Audioworm]

Oh when I typed in Stealth as a perk suggestion I meant "You can get closer to enemies without alerting them." Fixed that.
Anyway, another perk:

Martyrdom: Drop an armed bomb when you die.(Pointless, but fun!)

New items:
Knife: Machete, but has lower range.
Crossbow: Like the bow only the arrows fly faster and travel farther.
Poison vial: Throw at an enemy to make them take damage over time. Does not do any direct damage.
Perfume: Damsels follow you if they start running.
Ninja suit(Already present in source, but does nothing): Allows you to crawl on walls and ceilings(Like in Tastes Like Spelunky).

[grieck]

I would think a weaker machete (knife) to be useless, as the machete is already Never worth taking with.

[DungeonPheonix]

A couple of perks:

Bloody Mess: everything that expels blood on death yields even more
Brightest Day: prevents Dark levels from occurring
Darkest Night: increases Dark levels' chances of occurring
Kick Me: fixes player health at 1, doubles money gained

If the Ninja Suit is to be added, it should probably take the place of the Climbing Gloves when equipped, at least.

[TheDoodler]

Ground smash: Upon taking fall damage a small wave occurs at the ground. Stunning and causing 1 damage to anything it comes in contact with.

[Doolin]

Quick update, we're working on giving all monsters a xp value for the level system. Details to follow...

[grieck]

Bloody Mess: everything that expels blood on death yields even more
Brightest Day: prevents Dark levels from occurring
Darkest Night: increases Dark levels' chances of occurring
Kick Me: fixes player health at 1, doubles money gained

I fail to see the advantage of Darkest Night, though nice Fallout reference with the Bloody Mess.

[marsgreekgod]

Bloody Mess: everything that expels blood on death yields even more
Brightest Day: prevents Dark levels from occurring
Darkest Night: increases Dark levels' chances of occurring
Kick Me: fixes player health at 1, doubles money gained

I fail to see the advantage of Darkest Night, though nice Fallout reference with the Bloody Mess.

You can use it to get some other power mabey?

[Sageofrage]

Bloody Mess: everything that expels blood on death yields even more
Brightest Day: prevents Dark levels from occurring
Darkest Night: increases Dark levels' chances of occurring
Kick Me: fixes player health at 1, doubles money gained

I fail to see the advantage of Darkest Night, though nice Fallout reference with the Bloody Mess.

The only advantage to it I see is getting scarabs