TD → Auto-battler → SNKRX: a Mechanic Genealogy

…and where the proposed card-TD sits in it

This maps the family of games around the tower-defense trunk: which mechanics each generation kept, modified, invented, or dropped, and what design problem drove each mutation. The last section places the proposed card-TD (pre-map draft, mana per wave, hand of 5, draw 2 per wave, SNKRX visual style) inside the map.

1. The tree

WC3-era custom TD maps (Element TD, Gem TD, Wintermaul ~2003-06)
 │
 ├── Classic standalone TD (Desktop TD '07, Bloons TD '07, GemCraft '08, Kingdom Rush '11)
 │     │
 │     ├──→ Plants vs Zombies '09  ··· proto card-TD: seed loadout (deck), sun (mana), lanes
 │     │
 │     └── Wars TD (Wintermaul Wars, Legion TD ~'09, Squadron TD '11, BTD Battles '12,
 │           │       Legion TD 2 '21)
 │           │
 │           └── Auto-battler (Dota Auto Chess 1/2019 → TFT, Underlords, HS Battlegrounds '19;
 │                 │            Super Auto Pets '21)
 │                 │
 │                 └── SNKRX '21
 │                       ├──→ survivors-likes (Vampire Survivors '21, Brotato '22) — sibling formula
 │                       └── Mini Looper '26 (SNKRX × TD — the line re-acquiring the spatial layer)
 │
 └────────────────────────────┐
                              ▼
Card-game lineage (MtG '93 → Hearthstone '14 → Artifact '18)
                              │
                              ▼
              YOUR CARD-TD  ←─ chassis from Classic TD
                               organs (deck/draft/hand/mana) from the card lineage
                               precedents: PvZ '09, Monster Train '20, Ratropolis '20, Arknights '19
                               visual style: SNKRX

The key cartographic fact: the card-TD is a sibling of the auto-battler, not its descendant. Both are "TD + a randomized build feed." The auto-battler's feed is the shop — a distribution authored by the game. The card-TD's feed is the deck — a distribution authored by the player. Everything else about the two branches follows from that one difference (see §5).

2. The five generations, transition by transition

2.0 Classic TD — the root organ set

The genre crystallizes around: free placement on a path (or mazing), previewed scripted waves, a full tower catalog gated only by gold, kill-bounty economy, pay-to-upgrade tiers, lives lost on leaks, no opponent.

In micro/mezo/macro terms: macro almost pure. Zero execution (towers are the executors), zero hidden information, zero randomness in most classics. A fully visible fixed exam. The strength is legible spatial commitment — a maze is your lock-in drawn on the ground. The weakness is total solvability: the engine/coach cheat doesn't just help, it converts the player into a script executor, and the script works every time. (This is what per-map CHIMPS guides are for Bloons.)

2.1 Classic TD → Wars TD (the human exam)

Problem being solved: the fixed exam is solvable; replayability dies at the answer key.

• Added: a human opponent — creep sends, the income/investment axis (spend on economy vs defense vs aggression), value-timing reads. The exam becomes partly another mind: entity mezo arrives.
• Modified: Legion TD's pivotal mutation — towers become fighters. You place units during a build phase; they unroot and battle the wave. Build phase / combat phase alternation = the auto-battler round skeleton, fully formed years early.
• Dropped: mazing shrinks to build-zone formations; the solitaire pacing goes (rounds now synchronize across players).

2.2 Wars TD → Auto-battler (the shop transplant)

Problem being solved: Legion's build menu still tier-lists — with the full catalog available, build construction is lookup; and the WC3/SC2 client dependency caps the genre.

• Added: the random shop (offer slots, reroll, lock) — build construction becomes per-run inference; 3-copy merge (upgrades become probability events instead of purchases); interest + win/loss streak economy (economy becomes commitment timing); tagged trait/class thresholds (synergy goes designer-explicit); shared finite unit pool; scouting opponents' boards. Two mezo organs in one transplant: aleatory (shop) and entity (mirror PvP — the exam is the other seven players' builds).
• Modified: spatial play shrinks again — from build zones to grid arrangement (front/back, corners).
• Dropped: mazing/path entirely; creep sends (PvP damage is now your surviving units, not purchased aggression); the persistent tower object (units are bought, sold, rolled like cards).

2.3 Auto-battler → SNKRX (the micro transplant)

Problem being solved: spectator combat — zero agency once the round starts — plus the lobby/queue weight of 8-player PvP.

• Added: continuous steering — the player becomes the positioning system in real time. Positioning, which the auto-battler had reduced to a between-rounds grid decision, becomes a moment-to-moment verb. Micro re-enters the family for the first time since the root.
• Kept: the entire auto-battler economy — random shop with reroll/lock, gold + interest, copies-to-levels, class thresholds.
• Dropped: PvP (the exam reverts to scripted PvE waves with NG+ scaling — back toward the root), the grid, scouting, the counted shared pool.

The survivors-likes (Vampire Survivors, Brotato) run the same formula — auto-attacking arsenal + offer-draft + PvE waves + steering — concentrated into a single body. Mini Looper is the SNKRX line re-acquiring the TD spatial layer from the root.

2.4 Root → Card-TD (the deck transplant — your branch)

Problem being solved: the shop is a storefront — the game authors the distribution you draw from. Moving authorship to the player (deck construction) buys: pristine attribution (every bad draw is variance against a distribution you built — deck wrong, sequenced wrong, or variance, the poker triad), a front-loaded draft skill, and the hold/play hand reads that shops don't have.

• Added (from the card lineage): drafted deck → shuffled draws; hand of 5, +2 per wave; mana per wave as the spend constraint; improvement cards (upgrades become aleatory deliveries).
• Kept (from the root): full spatial placement, scripted previewed waves, lives. The two organs the auto-battler line abandoned — the maze and the static tower — come back intact.
• Absent (so far): all the auto-battler organs (shop, merge, interest, traits, pool) — available as ports, see §5.3 — and any micro.

3. The full mechanic matrix

Status is relative to the column's parent. Card-TD's parent is the root chassis; its NEW cells arrive from the card-game donor lineage.

Micro/mezo/macro coordinates per node:

4. The constellation — what each neighbor proves or warns

• Plants vs Zombies (2009) — the proto card-TD, and proof the chassis hybridizes: seed loadout = fixed deck (no draws), sun = mana, cooldowns = pacing. What it lacks is exactly what you're adding — draw RNG and a real draft. PvZ shows the fairness of the form; your additions supply the mezo.
• Monster Train (2020) — the nearest realized relative: deck + hand + mana + lane defense, drafted during the run against varied encounters. Proof the full system works and stays alive for hundreds of hours. Note what it does differently from your spec: interleaved drafting and a non-fixed exam. That difference is the whole collapse question.
• Arknights (2019) — the cautionary neighbor: drafted squad + mana-like deployment points + true spatial TD, but no draw randomness and fixed exams. Result: the endgame is guide-following — per-stage video answer keys. This is your design with the aleatory layer removed; it demonstrates precisely why the card layer needs draws.
• Ratropolis (2020) — real-time card-driven defense; proof the hand-under-pressure loop works in real time, at some cost in legibility (chaos at high speed).
• Legion TD 2 (2021) — the wars branch alive and standalone; the income/send axis remains the deepest economy-as-aggression design in the family if you ever want a competitive mode reference.
• Super Auto Pets (2021) — the auto-battler reduced to its minimum organs (shop, merge, async PvP); useful as proof of how few parts the shop engine needs.
• Survivors-likes — what happens when the SNKRX formula concentrates into one body; relevant mostly as the genre your card-TD is deliberately not (no micro).
• Mini Looper (yours, 2026) — SNKRX × TD with steering. The boundary matters: see §5.4.

5. The card-TD analysis

5.1 Lineage position

A sibling branch of the auto-battler: both transplant a randomized build feed onto the TD chassis. The auto-battler's feed is game-authored (shop) and came bundled with PvP; yours is player-authored (deck) and stays PvE. Because it branches from the root, it recovers the two organs the auto-battler line lost — the maze and the static tower — and skips the organs the auto-battler invented (those remain portable, §5.3).

In the micro/mezo/macro frame: macro-heavy on two independent layers (spatial placement + deck construction), mezo entirely aleatory and self-authored (draft commitment + draw order + mana sequencing — the cleanest attribution profile in the family), micro zero. Nearest framework neighbors: Hearthstone/Artifact territory, but with TD's spatial macro substituting for the opponent. One honest description: single-player Artifact where the opponent is the wave schedule — deck, mana, hand, board, no execution layer, judged by variance.

5.2 The novel interaction

Spatial irreversibility × draw uncertainty: placing a permanent, lossy-to-undo tower whose value depends on cards not yet drawn ("building the socket before drawing the gem"). Card games can't produce this (boards are cheap to rearrange); TD can't (the catalog is always available). This bet type is the design's identity — protect it.

5.3 Organs on the shelf (auto-battler parts, card-frame translations)

5.4 Risks, from the map

1. The Arknights collapse. Fixed map + fixed waves + known deck → per-map deck tier lists + contingency flowcharts → guide-following. Draw variance against a fixed exam perturbs means, not goals — it jitters the timing of a known plan. Mitigations, in increasing order of cost: partial exam preview at draft time (draft against wave types, not the full schedule); interleaved drafting (draw 2 + draft 1 per wave — restores the pick→evidence→pick loop); exam-side variance (wave drafting, procedural maps). The Monster Train–Arknights delta is exactly this dial.
2. The decorative card layer. If mana and draws are generous enough that you can always afford an answer and always have one, the deck degenerates into a slow catalog and the design is "TD with extra steps." Monster Train avoids this with genuinely tight mana and real scarcity. Starvation is load-bearing.
3. The Mini Looper boundary. Card-TD with a steerable hero = Mini Looper with extra steps; the two projects blur. The card-TD's identity is the no-micro, deck-driven corner — Artifact-vs-environment. Keep the verbs disjoint: Mini Looper steers, card-TD schedules.

5.5 Open design dials (each small, each governs a lot)

• Draft timing: all pre-map vs interleaved per-wave (the collapse-rate dial).
• Exam visibility at draft: full schedule / wave types only / map only.
• Mana carryover: none vs banked vs banked-with-interest.
• Resource count: mana only, or mana + kill gold as a second currency (kill gold preserves the root's "defense funds defense" loop; mana-only is cleaner but cuts the TD economy organ entirely).
• Playset rules: singleton / limited copies / free — interacts with merge-on-duplicate.
• Hand limit + discard: whether holding has a price (discard decisions = pricing future variance).
• Micro: none (recommended for identity) vs minimal (manual ability casts à la classic TD actives).

5.6 The visual-style note

The SNKRX skin is semantically honest here, not just convenient: the genealogy means the units are the same family — class-colored shapes, the same enemy vocabulary, the same flat-arena legibility. Towers as SNKRX-style circles with class colors, cards as the only new UI surface (and the SNKRX UI toolkit in snkrx-template/ already has card, slot, cooldown, and bar widgets to build it from).