Dragonsweeper

Nope, it's all about careful (or sometimes carefully risky) play. You should try to save breaking blocks for the endgame, for example. Also heart scrolls always give you full health, so they're worth more when you have more heart containers. Learn the patterns of the monsters; try to learn how to guess where the rat king or slime king will be. Things like that.

Yes, there is enough HP to complete it 100%, and no, there’s no max to exp you can have at once. I suspect the problem you had is that you used the heart scrolls too early on. Since they always refill you to max HP, they’re worth a lot more if you hold them until you have higher max HP. In particular, if you get to 0 HP and you have enough exp to level up, you should always do so rather than using a scroll.

It’s actually only one gnome. When you click on him while there are still any empty unrevealed squares, he’ll teleport away to one of them. Once there are no more such squares, you actually catch him and get his 10 XP.

That’s why I usually kill the dragon immediately once I get 13 hearts for the first time.

The problem is that gamelib.js calls the getImageData() method on a canvas that has data loaded from an external image file, which falls afoul of https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/getImageData#exceptions and https://developer.mozilla.org/en-US/docs/Web/Security/Defenses/Same-origin_policy#file_origins when the game is running from a file:/// URL. To work around this, either set up a local Web server and then run the game through localhost, or go into gamelib.js and replace this block of code:

                    let r = (colorMultiplier >> 16 & 0xff)/0xff;
                    let g = (colorMultiplier >> 8 & 0xff)/0xff;
                    let b = (colorMultiplier >> 0 & 0xff)/0xff;
                    let imgData = ctx.getImageData(0, 0, cellw, cellh);
                    for(let i = 0; i < imgData.data.length; i += 4) 
                    {
                        imgData.data[i + 0] *= r;
                        imgData.data[i + 1] *= g;
                        imgData.data[i + 2] *= b;
                    }
                    ctx.putImageData(imgData, 0, 0);                

With this one:

                    ctx.fillStyle = "#" + colorMultiplier.toString(16).padStart(6, '0');
                    ctx.globalCompositeOperation = "multiply";
                    ctx.fillRect(0, 0, frame.rect.w, frame.rect.h);
                    ctx.fillStyle = "black";
                    ctx.globalCompositeOperation = "destination-atop";
                    ctx.drawImage(img, frame.rect.x, frame.rect.y, frame.rect.w, frame.rect.h, 0, 0, frame.rect.w, frame.rect.h);
                    ctx.globalCompositeOperation = "source-over";

Congratulations! I'll try to do it too.

That can only happen if you do not use any health refills until you’ve […] cleared out all mines.

There’s actually a little bit more leeway than that: your first health refill needs to be when you have 11 hearts, and you can get to 11 hearts by clearing only the first 6 of the 9 mines.