As pointed out by others, the first three minifigures are genuine LEGO (with the second having perhaps a few custom accessories). The fourth is not a LEGO minifig. It may include some genuine LEGO elements (legs, hands, etc), but the militaristic accessories are not LEGO elements. This appears to be a custom minifig sold at one time by Modern Brick Warfare.
These came from a number of sets, including a handy "Decorated Elements" set that covered most of the printed parts from the mid-90s space theme.
However, Recon Robot appears to be the only one that contains two of the 2x2 tiles and only one of the 2x1 tiles.
Instructions can be found in a number of places, including on Let's Build It Again.
I actually managed to find the exact set while refining the question. It's set 744, released in 1980.
Here are the reasons why the research I did prior to writing the question didn't lead anywhere:
The yellow motor does not show up when searching parts on BrickLink. It's probably because on the list of set 744 parts, it has a note saying "Part colour ...
That white snake appears in two sets, and in quantity either one or two. My best guess is that it was from a Pick-a-Brick wall at a Lego Store, or something very similar. I'm basing this on the many, many repeated pieces.
These bags don't seem to belong to any specific LEGO set.
First, they are filled very sparsely. Normally LEGO bags are filled with more elements than that depicted here.
Secondly, in bag #3 we clearly see a Plate 6X6 W. Bow in medium lilac:
And a Right Plate 3X8 W/Angle in bright yellow:
But these two parts have never been sold in the same set. These ...
Those horses look like legit LEGO-brand horses.
White Horse with Black Eyes, White Pupils and Dark Orange Bridle Pattern: 4493c01pb04
Black Horse with Black Eyes Circled with White, Brown Bridle Pattern: 4493c01pb02
In order to be extra sure they are genuine LEGO, look for the "LEGO" stamp on the inside of the hollow studs on their back ...
Both sets are from 2014, which is why you couldn't find them on LEGO website.
Elements included in first picture and first three polybags on second picture are from Battle Towers (21205) set.
Identified by unique modified printed tile.
The rest looks like it comes from Forest Animals (31019)
Identified by round 2x2 tile with eye pattern together with round ...
Find for the rarest piece(s)
My usual method for identifying a set I'm not familiar with is to find the rarest part. It's not always possible to find the rarest part but I can usually guess which parts are rare given how many of them I have in my collection.
For System sets I will usually ignore unmodified bricks, plates and tiles in common colours.
It looks like the bulk of the parts are from The Chamber of Secrets (4730):
As Henrik mentioned, Sorting Hat (4701) is also present:
Jason pointed out that Dumbledore's Office (4739) is also present:
I thought it might be worth noting that these old Harry Potter sets are fairly valuable to collectors. The Chamber of Secrets alone in complete used ...
The most obvious sign is the LEGO mark present on each stud*. I have yet to learn of any single copycat company that would go through the legal and technical trouble required to mold these onto every stud of every piece in a consistent fashion.
If the piece has no studs to check or the markings are present and you still have doubts you can take a suitably ...
Most of this looks like it's part of the Mars Mission range - however, none of those sets contain the 2 flames, and the Minifig has both wrong colour torso (grey, instead of white), and the wrong type of helmet (he has Headgear Helmet Space instead of a Motorcyle Helment)
As for which Mars Mission set you have there, from curved Windscreen, the Technic bars ...
You’re correct that the one set looks like Hogwarts. Specifically 5378 Hogwarts Castle (3rd edition). There are three Dolores Umbridge figures, only one with solid pink legs like in your photo. This version only appears in the 3rd edition Hogwarts.
The Star Wars set looks like 8039 Venator-Class Republic Attack Cruiser.
Neither set contains Boat, 14 x 5 x ...
The red car that you mentioned is Mail Van (7820).
There are a number of other trains in the picture including:
7730 - Goods train (the locomotive doesn't seem to be visible)
7710 - Push-Along Passenger Steam Train (just the cars)
7750 - Steam Engine with Tender (pulling the cars from 7710)
7814 - Crane Wagon
7760 - Diesel Shunter Locomotive
7720 - ...
These appear in 4s in many iterations of the Imperial Shuttle, and also many of the X-wing, as well as the
MT-201 Ultra-Drill Walker and the SP Undercover Cruiser. I can't say for certain which of these sets originally contained those pieces, but this should get you closer. This list also shows sets that contain the piece in smaller quantities.
I think that is 7937 "Train Station"
I recognised the white girder piece as being in the Saturn V set
Bricklink then shows all other sets with that piece
Of the eight sets that have that piece in white, the 7937 also has two blue chairs and some grey ladders.
These items are from different sets.
Let's begin with the most obvious - minifigure. It is a Royal Guard from Star Wars and there are couple of versions of them. Yours seems to be with arms and hands in Dark Red. Yet, there are still two version of them (depends on the type of cape you got):
Royal Guard with Dark Red Arms and Hands was part of two sets in ...
These are identified from left to right.
Series 18 of Lego Minifigures has that first policeman. Here is the exact minifigure.
The second one appears to be from Series 9 of Lego Minifigures. Here is the exact minifigure.
The third policeman appears to be LEGO Policeman with Riot Helmet Minifigure with a different head. The head might be Minifigure, Head ...
This game represented the LEGO Designer Sets (Make & Create) from 2003–2005, and so the majority of models are based on them (WB1 models are from the first and second waves, and WB2 the third wave). As someone who grew up with the game and the Designer Sets as a tween, and still has many of them built to this day, I believe I can answer this question ...
Left Plate W. Angle 3X12 only comes in Bright Red in 6 sets. Only 1 set also contains this piece in White.
31047-1: Propeller Plane
This set also contains:
403224: Plate 2X2 Round in Bright Yellow
4560179: Flat Tile 2X4 in Bright Red
4211440: Technic Brick 1X2, Ø4.9 in Medium Stone Grey
6083620: Cross Axle 4M With End Stop in Dark Stone Grey
So both bags ...