Last Asylum: Plague Rat Swarm Guide – How to Beat the Rat King

Want to beat the Rat King without wasting your budget?

Most heavy spenders get stuck not because they spend too little — but because they spend wrong.

This guide shows you exactly where to put your money for the highest return: which heroes to max, which towers to upgrade, and how to clear faster with zero wasted resources. Let's get into it.

 

What Is Rat Swarm?

Rat Swarm is Last Asylum: Plague's core PvE tower defense mode.

• Waves of infected rats run fixed paths toward your Sanctuary
• You build and upgrade towers along those paths
• Deploy up to 5 heroes at strategic positions
• Survive until the final boss wave: the Rat King

So, hero placement, tower positioning, and ability timing — how well you coordinate these three things separates competitive players from casuals, and decides whether you beat the Rat King to unlock rewards, higher difficulty waves, and event scoring eligibility.

 

Why Heavy Spenders Still Get Stuck

It's not about spending too little. It's about spending in the wrong places. Three classic mistakes:

• Mistake 1: Spread Tower Investment Too Thin

Building towers evenly across the map dilutes your damage. The Rat King has massive HP. Spread damage = nothing dies fast enough = your heroes get overwhelmed in the boss phase.

• Mistake 2: Unfocused Hero Investment

Leveling 8–10 heroes moderately instead of maxing your core 3 leaves you with a roster that looks impressive but can't concentrate enough power to kill the Rat King.

• Mistake 3: Wrong Hero Roles for This Mode

Heroes that dominate in territory reclamation or PvP don't necessarily perform in Rat Swarm. This mode rewards sustained survivability + boss-phase burst.

 

Tower Investment Strategy

Core Principle

One fully upgraded choke point > five partially upgraded towers spread across the map

Why? Every rat passes through the choke. Every tower in range hits every enemy. Concentrated firepower = maximum total damage.

Priority	Tower Type	Why
1	Slow/Control (at choke entrance)	Gives all towers more time per enemy. ROI is multiplicative.
2	AoE Damage (behind slow towers)	Clears regular waves + chips the Rat King
3	Single-Target	Only for the Rat King phase. Low priority until your choke is fully upgraded.

• When Are You Ready for the Rat King?
  • If you're clearing pre-boss waves with comfortable margin → go for it
  • If you're barely scraping through the last regular wave → don't attempt. Go upgrade. Retrying wastes resources.

 

Hero Lineup

Core Three (Highest Investment Priority)

Role	Hero	Why
Tank	Arthur (UR) or Bella (SSR)	Arthur's team protection keeps everyone alive. Bella works if no Arthur. Tank star rank = most important investment
Main DPS	Marlena (UR) or Grenwald (SSR)	Marlena's scaling damage is top-tier. Grenwald has raw attack. Pick the one you have. Stack stars and abilities
Support	Stellar (SSR)	Monster damage buff + emergency heal passive. Don't invest first, but invest third

 

Flex Slots (Only After Core Three Are Maxed)

Slot	Option	Use
4th	Griffith (SSR)	Ranged tank + monster damage reduction aura. Critical for higher difficulty Rat King when one tank can't absorb everything
5th	Claire (SSR) or Bestar (SSR)	Claire = boss focus. Bestar = wave clear. Pick based on where you're struggling

*A maxed Arthur, a maxed Marlena, and a strong Stellar will absolutely crush five mid-investment heroes every single time. Depth over breadth. Write that down.

 

Spending Priority Framework (For $1,000+/Month)

Ranked by ROI from highest to lowest:

Priority	Where	Why
1	Highest Star ranks of core heroes (Arthur & Marlena)	Single biggest power increase for this mode. Direct hero shards and upgrade mats here first
2	Second Choke point tower upgrades	Once core heroes are set, dump all tower resources into one choke point
3	Hero ability upgrades	Ability levels scale multiplicatively with star ranks. Prioritize Marlena's burst + Arthur's team protection
4	Spread investment (widening your roster)	Useless for Rat Swarm. Save that for PvP or multi-team events

 

Conclusion

Rat Swarm isn't an execution game. It's a resource allocation game.

Whoever invests in the right places clears faster. Whoever spreads their money thin stays stuck longer. Run this framework. You won't need luck.