9 Kings Lab Rat: Levels, Adjacency and Current Builds

Lab Rat grows when adjacent plots level up. It is a Progress troop with no ordinary level cap. Its opportunity is repeated useful upgrades beside it; placing a Rat alone does not create a leveling engine. The priorities below are editorial suggestions for Patch #31 / 0.9.8, checked on 15 October 2026, without a measured difficulty clear.

The upgrade trigger

A neighboring plot must actually level. Playing an enchantment or discarding a card is a different action unless another eligible effect also causes an upgrade. Place a Rat beside a plot you expect to develop and compare its level before and after that upgrade.

Patch #29 explicitly added Patronage to the Lab Rat chain trigger. Patronage belongs to the Rainbow pool; it is an optional reward rather than an opening requirement. The same patch and its hotfix improved Lab Rat's initial stats, but did not publish a complete current combat-stat table. Historical HP and damage figures are therefore not presented as Patch #31 measurements.

A small connection plan

Put Lab Rat at B2 and an upgradeable useful plot at B1. A second useful plot at B3 supplies another possible connection. Keep enough immediate combat strength to reach those upgrades. Filling the surrounding spaces with support that never levels can consume land without supplying the intended trigger.

The Progress build uses Recycler at B1 and Lab Rat at B2. Upgrading Recycler can supply a neighboring level event; discarding a card separately gives Recycler's adjacent recipients its damage and HP effect. These are two different triggers. A discard is not itself a Rat level.

Current Reinforce changes the old build

Reinforce now supplies battle-time HP growth and can heal above maximum HP. Patch #29 replaced its earlier behavior. It does not turn every Rat level into the historical damage bonus described by old builds. Treat Rat leveling, Recycler growth and Reinforce survival as separate contributions.

If the Rat dies before developing, use a functioning defender or immediate upgrades. If it survives without enough damage, inspect the actual level events and offensive support. More future growth cannot repair a battle already lost.

Boundaries worth checking

The official reference describes no ordinary Rat level cap. That is not a claim of endless survival, unlimited safe turns or a guaranteed difficulty clear. Decrees, card availability and the current tooltip can change what an individual run does. Do not infer an exact multi-Rat chain formula or boss-conversion mechanic from the short reference text.

Sources and next decisions

The official card reference establishes adjacency and leveling. Patch #29 documents Patronage and the current Reinforce rework. Compare the Progress route, Recycler and build library.