Number Knight

There's a genre of ad you've probably seen wedged between rounds of a mobile game: a tiny knight in a tower, a bigger number standing in the next tower over, tap to fight, tap again, watch the numbers climb until you inevitably lose and get shown a store link. Number Knight, built by Adrien Guéret for js13k 2023 in a 13,121-byte zip, takes that fake ad completely seriously and turns it into an actual game — one with real rules, real difficulty curve, and no store link at the end.

A one-sentence pitch that hides a genuine puzzle

The opening levels teach exactly one rule: attack a monster with a smaller number than yours and you absorb its power; attack one with an equal or bigger number and you die. That's the whole game for about four levels, and then it stops being that simple. Killing an elemental monster means your next attack carries that element, and elements beat each other in a fire-beats-plant, plant-beats-water, water-beats-fire triangle — attack into a favourable matchup and your power counts double, attack into an unfavourable one and it's halved. A few levels later, skeletons show up that subtract their value from yours instead of adding it, wizards appear that buff every other monster in their tower the moment you kill them, and potions arrive that apply a flat modifier you have to calculate before you drink. None of this is explained in a single dense tutorial screen; it's staged one mechanic per level, in the same order listed above, which is exactly the pacing a puzzle this fiddly needs.

Reading the level data confirms there's no padding here — the game ships 29 distinct hand-authored towers (decodeLevel unpacks a compact string format like "25t+40mf_+40ma_+40mp_30wft100wp_ +80pm_+80amt-1000m" per level), plus one apparently unlisted joke level ("999t1") that only exists for the level-editor's own testing. There's no procedural generation propping up the count: every fight you're actually asked to solve was placed there on purpose, and the difficulty curve tracks the introduction of new monster types rather than just larger numbers.

Controls: a single tap, done right, arrives too late on a phone

Every action in this game is one tap on the monster you want to fight — there is no drag, no gesture, no secondary input to fumble on a touchscreen. Testing it with a real emulated touchscreen (not a mouse click standing in for one) confirms the tap lands cleanly on the target and the resulting attack animation, absorb, and camera pan to the next tower all fire correctly. On desktop the whole game — title screen, castle backdrop, and both towers — fits in a single 1280×800 view with nothing hidden.

On a phone-sized screen it's a different story for exactly the first impression that matters most. The tutorial's welcome banner ("Welcome to Number Knight! ... Click on this little blob to kill it!") renders in-flow above the game at narrow widths, and it pushes the actual tower — the thing you're told to click — entirely below the bottom of a 390×844 viewport. The page is natively scrollable, so a player who thinks to swipe up finds the towers waiting for them about 117 pixels down, but nothing on screen suggests that's necessary; the tutorial text describing what to click is visible while the thing it's describing is not. This is exactly the class of problem this section exists to catch, and to the developer's own credit, the js13k submission page says as much up front: "Even if it's optimized for desktop, the game should be playable on tablets and smartphones. But have in mind the experience is a bit degraded on small screens!" That's an honest disclosure, and testing bears it out — the degradation is real but recoverable, not a dead end.

Separately, a burst of successive taps fired fast enough to overlap the attack animation once produced an uncaught Cannot read properties of null (reading 'childNodes') error in the console. Play resumed normally afterward and no state appeared to corrupt, but it's a sign the input handling assumes a slower, more deliberate tapping rhythm than an eager mobile player is likely to give it.

Presentation and content

The pixel art (Kenney's assets, edited, plus purchased tower sprites from BlackSpire Studio) is clean and reads well even at the small scale a phone forces on it, and the procedurally synthesised chiptune hits and music — all hand-written waveform functions, no audio files — sound properly retro without any external dependency. There's a level editor built directly into the game, letting anyone construct a custom tower layout and generate a shareable link, with an optional (and, per the author's own description, occasionally slow-to-sync) Pinata IPFS backend for saving levels without an account. It's a genuinely nice bonus for a jam game, and js13k's own "Decentralized" bonus-category judging placed it 3rd for exactly that feature, while the main competition ranked it 6th for Controls and 16th for Gameplay across that year's field. Those numbers back up what the tutorial pacing suggests on its own: this was built and iterated with real care inside a 13-kilobyte budget.

Final verdict

Number Knight succeeds at the thing it set out to do — take a format everyone recognises as a cynical ad and build a legitimately interesting tactical puzzle out of its bones — and it does so without a build step, without any analytics, and under an open licence that costs the shelf nothing to host. The campaign is short and the element-matchup rule needs a reference the game never gives you, but neither is disqualifying. What keeps this at a 7.5 rather than higher is the phone-specific onboarding problem: the first thing this shelf promises is that touch works, and here it does — eventually — but only after an unprompted scroll past the very tutorial text telling you to tap something you can't yet see. That's a real, fixable rough edge, not a broken control scheme, and it doesn't survive contact with the rest of the game once you're past it.