I am not able to solve even a single puzzle :(

Read the rules carefully, multiple times.
Try to find openings, applying the rules.
Try to think "If .... then what happens, is any rule violated."
And if you are stuck, save your work and come back later.

I have a little question about puzzle 10...
In the requested sentence there are two "I' 's and one time the digit 1. But it looks like there are three same characters "I" (or 1?) in the grid? Could all three characters be used for the digit 1?

1 can be any of the three "I". Two other "I" will be letters.

Just to make sure -- in "Tools", the answer key only describes whether the edges of the grid along the given row or column are occupied (and if so by what tool) or not, correct?

More precisely: what would be the answer key for the second row in the example? Am I right that it would be -----HH---- ? (i.e. the edges that are "inside" the ladder are unoccupied and so remain "-" in the answer key, even though there is a ladder) ?

Yes, for the second row in the example the answer is recorded correctly.

Just a small confirmation for #10 (April Contest 2015 At LMI):
At the points of intersection, the line path must always continue straight ahead, it cannot have 2 turns (reflecting off each other)?

The line path must always continue straight.

V zadanii 10 v forme dlja otvetov ukazyvaetsja na moju oshibku pri opisanii marshruta. Posle ukazanija poslednego ugla nichego ne nuzhno ukazyvat'? Ved' mozhet byt' nejasno napravlenie i dlina otrezka!

Ne nuzhno, ja dorisuju hvostik linii.

Player3 grid has 8 solutions. It has six rows of "LOOLOOLOO", and 3 rows of "CLLCLLCL?", where "?" can be C or L.

Thanks James. What about Player13?

The Player13 grid is interesting.
The only way to get four adjacent 200s is with:
LOLOOLOOL
OOLLLOOLO
OLOOLLLOO
LOOLOOLOL
or its mirror image. (this is not simple to prove!)

So that fixes the top 4 rows, and if the bottom 4 are the same pattern then the solution must be:
LOLOOLOOL
OOLLLOOLO
OLOOLLLOO
LOOLOOLOL
LCLLCLLCL
LOLOOLOOL
OOLLLOOLO
OLOOLLLOO
LOOLOOLOL

If the mirror image option is used below then no solution is possible.

So the Player13 grid is fine.

In puzzle 10, minimizing P+2E. I thought E means the number of empty cells through which the thread moves...

I saw it more April 10. Do not have a unique solution puzzles of other participants. I ask everyone to look at the preliminary results and report if something disagree.
I congratulate James, Tomoaki and my Ukrainian friend Sergey with a victory in the April contest!

I counted the puzzle10 is easiest to understand. In any case, thank you for your participation!
I thank everyone who participated in the contest and Deb, Prasanna and Rakesh for support!

Thanks Riad for many wonderful puzzles. These were certainly very difficult and had me frustrated for many hours! With so many unique rules, it was easy to make a careless mistake early on in a puzzle, not be sure where you had erred, and have to restart. But, it was certainly fun and had me focused intently for a long time. Unfortunately ran out of time to tackle the last optimiser!

On the results: it looks like I did not receive any points for my COOL optimiser, and Christian may have been given the points in my place. Thanks again.

Unfortunatly for me, I was Player3, and I made the wrong choice :(
I had also the idea to send your solution (the good one) but I thought mine was easier to check, and I checked mine... too quickly.
Because of many players found the best solution last year on Roman OX, I thought the same players will find easily Roman COOL, which is a kind of transposition... And because of this transposition, I was early convinced that 1200 was the best score to reach.

Definitely, I was too lazy this time : for puzzle 10, I have the same answer than Hugo, and didn't saw your answer, which is so similar :((

Congratulations to all, and espacially to Riad for the conception and to James for his performance !

I saw that in your puzzle is not the only 1 solution. I noticed that if you moved down the 150 in the middle row, then the solution would be the only one. I cooked your puzzle in PDF-file with your answer. Alas, the answer was the same as in the file. I wish you good luck in the next contests!

Thank you Puzlifouk,
Your puzzle I checked the day before the end of the contest. I thought that you can still move the 150 to the right and correct the last day of the contest. But your idea really was good.
See you in September, I have already prepared a contest of new puzzles!

Hi Riad, not sure I understand. I submitted: 1800#150,150,-,150,-,150,-,150,150,150,150,-,150,150,-,-,150,150#-#-#-#-#-#-#-#-#- (Player 8) and pretty confident it has a unique solution!

A new pdf has been uploaded with actual player names.

Hi Orion, sorry, now I see that you are right. I added you points.

Thank you Riad for another great contest.
The puzzles are hard, but we have a week so that is not a problem. It is nice to sit down and solve a puzzle without time pressure.
I kept making small mistakes in the Mirrored Sudokus, I solved it on my 3rd try.

For Optimizer #10 I found 6 solutions with 9 points, and there are 2 more in the pdf. I think this was just hard to find any solution, especially in the bottom-right corner. I expected many people would find 9 points.
But I thought Optimizer #11 was the hardest. On the last day I submitted a 2225 solution, which is the best when going around the edge. Later that night I tried the "S" shape and found the 1818 solution. I thought this would be very hard for people to find, but 14 people did! Great work by all of them. This was my favourite puzzle.
For Optimizer #12 I remembered last year's Roman Ox, which I did not do well with. First I found a symmetrical "tartan" solution, with 6 clues on the top and side (150,-,150,150,-,150,150,-,150). Then I removed one clue at a time, checking for uniqueness, until only 8 clues remained. This surprised me, I thought 10 clues would be minimal. Also surprised that less people tried this.
I looked at solutions with three adjacent clues (e.g. 150,250,200) but these were too expensive for not enough information.

Well done to Tomoaki and Sergey also.
Every year I feel very lucky to win this, maybe next year my luck will finish :)