Puschkin

That's not what I said. In fact, if you are on a budget, it's even more likely to face fast aggro decks! You don't need expensive rares and you don't need to use much brainpower to assemble a strong aggro deck that should wipe the floor with decks that can't defend themselves like yours. All you have to do is to pick a tribe, guild or block mechanic and then start adding creatures that boost each other, following the mana curve. For discussions sake let's take soldiers as an example (and please note that I usually don't build tribe decks because they are not challenging to build):

For turn one I'd have something like Champion of the Parish or Boros Elite. They start out as 1/1s but get stronger later automatically.
For turn two I add a mix of Precinct Captain, Auriok Steelshaper (if I am going to add equipments) and Veteran Armourers.
For turn three I could have either a Veteran Swordsmith, Crusader of Odric or Field Marshal.
On turn four I could equip the Steelshaper, cycle a Gempalm Avenger or play a Daru Warchief.

Now calculate how much damage I do if I attack each turn. No matter what combination of creatures I played, you'll be dead by turn four. And the thing is: This deck won't even run out of steam later in the game because there is still room fore more expensive stuff and because it doesn't matter which one you draw, they all boost each other. Especially if you play with equipments, you can recover from board sweepers very fast.
Please note that the Field Marshal is by far the most expensive card in here with about 4 dollars, the rest is about a dollar or a few cent.

I don't like this, too, but that's what Magic has become. But even if it wasn't for stup tribes and block mechanics, just do the math for simple vanilla creatures:
Turn one: generic 1/1 creature
Turn two: generic 2/2 creature or two 1/1s => attack for 1, total damage 1
Turn three: generic 3/3 creature or one 2/2 + one 1/1 => attack for 3, total damage 4
Turn four: generic 4/4 creature or combination of smaller creatures => attack for 6, total damage 10
Turn five: Attack for 10, total damage 20 !!!

See? You are dead by turn 5 and all I did is playing a creature each turn that has a power of equal to it's casting cost. Those creatures don't have any abilities and I didn't play anything on turn 5. This means you'll lose against a deck full of Dwarven Ponies, Grizzly Bears, Centaur Coursers and Rhox Brutes, a deck that needs zero skill to assemble and where the sleeves are more expensive than the cards.

So, maybe the decks your buddies play aren't bad but in that case they are SLOW. You are probably all used to play slow decks that they don't seem to be slow to you and adapted your play style, so you can get away with a deck like this that can't block or kil creatures for 5 consecutive turns but please realize that you seem to play in an environment that is radically diffrent from ours and thus, it is very hard to make proper suggestions.

It's actually Legacy but you are aiming for Modern now?
You could up either the Giant Growth or the Probe to 4 and call it a day.

When I said you could go down to as low as 16 lands you didn't have any cards above 1 mana besides those 4 Stalkers. So, with just 16 lands now I think you cannot support the Invisimancer. Keeping Aqueous Form 4 of was the right choice, the Gitaxian Probe is a nice way to decide when/if to go in for the kill, great idea. But I am unsure if the addition of the Tusker is worth the trouble of running a GG creature ... you might be better off replacing them with Ledgewalkers as well. But that's something to decide after playtesting, I guess. So, final adjustment would be to ditch the Invisimancer for something you want to try out, maybe a Sigil of Sleep? Maybe for a 17th land (even without the Invismancer the deck is slightly more expensive now).

Deadapult?
When I read the deck title, I thought Deadapult was the key card ...
I also question the necessity to splash white.

There is no red 6/6 flyer for 4 mana at all. Gothy probably dreamt that up.

So you are playing against ultra slow and/or bad decks all day. That makes it actually difficult to make suggestions for your deck because in that case you could probably win with anything. The power creep of the recent cards is so intense that even if you play multiplayer (which is usually slower) you can't afford to sit there witzhout defenses for 5 turns anymore. Every second guy plays a tribal deck of sorts these days and most tribes have cheap creatures for every mana slot with effects that make each other stronger. By turn 4 you can get overrun but all kinds of nasty stuff without that player running out of steam in late game.

Anyway, if it works for you, fine, but you would get slaughtered in my play group. Especially in subsequent games where people know that you are running Pandemonium. Basically, everybody has 4-5 turns to eliminate the Pandemonium player before things get silly and that's what everybody with brains will do. You might sneak in a win the very first game you play because you don't look threatening but once a Pandemonium has been sighted it'll be raining damage.

Card search says such a creature doesn't exist.

Shattering PULSE is what we are talking about and what your deck list says. And if you use that buyback rarely, Shattering Pulse is NOT good enough. Shattering SPREE on the other hand is a good example of a spell that could replace the Pulse because it's strictly better if the buyback is never actually used; so are Fury Charm and Echoing Ruin.

Really? What kind of decks are you playing against that you don't need it, decks that play their first creature on turn 6? I mean, the Fireboar is the only creature you have that can actually block and it won't be out before turn 5, you also don't have any early burn or spot removal. This means you would probably lose against any creature based deck that follows the mana curve and plays a creature every turn, even if those are vanilla creatures.

Maybe this would finally be a red deck that could make good use of WALLS. Wall of Razors would fit this deck perfectly because it still works well later with Pandemonium.

Maybe Meekstone instead of Smoke.

Ruby Medallion instead of Coldsteel Heart.

Use something else than Shattering Pulse, since you are constantly replaying your creatures you won't have the mana to play it with buyback. For example Smash.

Similarily, with just 20 lands to support all of this I don't see you having the mana and time to make use of Scrying Sheets.

That's still a gamble and if you DO wait for a single attack, you'll need even less cards to make creatures unblockable. Heck, if that single creature is the Stalker, you don't need any additional cloaking! That's why I suggested Silhana Ledgewalker and Rancor to replace some of the cloakers. And either way you don't need 20 lands, at least not when you can afford to run Breeding Pool or at least Yavimaya Coast.

Except that:
* He has only 16 creatures but 24 cards to pump and make them unblockable. As a rule of thumb, you pumpers and enhancers should never outnumber your critters or you'll constantly run into situations where you have a handfull of pump but no creature to dump it on.
* 12 of those cards are used to make them unblockable which is only useful if also have a pump spell the same turn which will not be the case many times. Especially since none of your pump is continous. Aqueous Form is permanent, DIstorting Strike and Artful Dodge can be used twice, the Stalker is already unblockable, you really, really don't need 12 of those cards!
* The deck has only 2 cards that cost more than one mana and no card draw. You'll run out of steam quickly, especially considering the problems above. You need to attack with a pumped creature at least 4 times, maybe 5 times, you should be able to see the problem now. You'll need 4-5 pump spells, about 2 maybe 3 cards to make them unblockable, at least one creature (but most likely more because you will be forced to block at some point) and at least 2 lands. That's a minimum of 9 and a maximum of 12 cards. If you go first and want to win by turn 4-5 you have drawn 10-11 cards. Which means those cards have to be EXACTLY what you need! And all of this is best case scenario where your opponent doesn't interfere other than playing potential blockers, if he has counterspells, board sweepers, Fogs or any other way to deal with you, you are done.

My recommodations:
This deck screams for Rancor! It may pump only for 2 and the trample seems redundant, however, it boosts the power permanently and comes back if your creature happens to die, saving you cards.
The deck, as it is, doesn't need 20 lands! But it probably needs some sort of dualland that doesn't come into play tapped to make sure you have both blue and green first turn.
Removing about 2-4 lands and reducing the number of unblockable-enhancers makes room for the Rancors and another creature, something like Silhana Ledgewalker (which has hexproof and is already almost unblockable, all you need it pump).
For the sideboard I recommend Sigil of Sleep to solve any problems you might have with too aggressive creatures on your opponent's side.

Playing the opponent out of cards.

Ah, got it. Coolwip just confused me with his "you would have to pay one mana you want a creature back" part. Myr Retriever only works on artifacts, so I automatically assumed 3 and 5 are the ones with the dual Retrievers :)

Read the cards again. Retriever immediatedly dies because the Heartless Summoning gives it -1/-1. And it reduces the casting cost by 2. So, Myr Retrievers cost 0, die as soon as they hit play and every time this happens, one returns the other one from the grave to your hand.

As a rule of thumb, you should always have more creatures in your deck than cards that pump your creatures. Otherwise you'll sit there with a lot of pumpers in your hand but no target to play them on.
And please elaborate on your selection of creatures and pumpers, it's hard to tell what you are trying to do. Gift of Orzhova and Unflinching Courage work well on the Fencing Ace but apart from that, your selections look quite random. The Goliath looks good on paper but wuth just 20 mana sources you will very rarely be able to use that scavenge. The Serra Avatar has a severe drawback, especially in a creature light deck like this.
Also I am pretty sure Essence Harvest is not worth splashing black into this, especially without any sort of duallands or mana filters.

Curfew is more fitting, thouogh.

I agree with JonBomb. Also, Spore Cloud would be better than Clinging Mist. And I would also replace the plain Fog with a mix of Constant Mists and Moment's Peace. Seriously, there are many Fog variants out there that are better than your picks.

All I am saying is that you should maybe drop one combo component (and reduce the viable combos to 4 or 3) and add tutors/library manipulation instead.