- Undertale Adventures unit upgrade decisions should follow role value, not rarity alone
- Concentrate upgrades on one well-positioned core unit before spreading levels across the map
- Damage carries first: rerolls and upgrade currency go to permanent core units like Sans or Undyne
- Support units: upgrade Toriel only when survivability actually blocks your clears
- Starter units: keep Frisk and Papyrus upgraded just enough to farm early stages
How Unit Upgrades Work in Undertale Adventures X
Undertale Adventures X follows a classic tower-defense loop: place Undertale-themed units along the enemy route, earn currency during waves, and spend it on upgrades that improve damage, range, or attack frequency. An upgrade is only as valuable as the position and role of the unit receiving it, so planning matters more than raw spending.
Upgrade before expanding. A fully upgraded unit covering a long section of the path will consistently outperform several under-leveled units scattered across placement slots.
The upgrade system rewards three things:
- Positioning quality: units near corners, bends, and shared paths attack more often per wave
- Timing: upgrading right before a difficult wave prevents leaks better than reacting after
- Role clarity: damage dealers scale best with offensive upgrades, while supports need consistency instead
| Upgrade Factor | What It Improves | Priority |
|---|---|---|
| Damage | Kill speed against tougher enemies | ★★★★★ on carries |
| Range | Path coverage and placement flexibility | ★★★★ on lane units |
| Attack Speed | Attack frequency during dense waves | ★★★★ on repeated-hit units |
| Survivability | Stability during sustained pressure | ★★★ on supports |
Unit-by-Unit Upgrade Value
Each unit in the roster has a different payoff curve for upgrade investment. Use this breakdown to decide where your in-stage currency and long-term resources should go.
Sans - Top Investment
- High-impact damage and control
- Best when enemies survive multiple attack cycles
- Scales strongly with upgrade investment
- Best for: late-game stages, boss-focused encounters
Undyne - Core Carry
- Reliable sustained damage
- Consistent across repeated waves
- High upgrade value for general progression
- Best for: normal stages, long survival waves
Papyrus - Early Value
- Early and mid-game damage
- Medium-to-high value before premium units arrive
- Keep upgraded while building a specialized roster
- Best for: opening content, early farming
Toriel - Situational
- Defensive support utility
- Upgrade when survivability blocks clears
- More valuable in a complete team than solo
- Best for: sustained-wave pressure stages
Frisk - Starter Tool
- Learning and gap-filling unit
- Most valuable at the start of progression
- Reinvest into stronger units later
- Best for: first stages, formation testing
Flowey - Flex Slot
- Flexible roster option
- Judge by actual stage performance and cost
- Useful for testing formation layouts
- Best for: early normal stages
| Unit | Role | Upgrade Priority | Replace When |
|---|---|---|---|
| Sans | Damage and control | High - late-game carry | Rarely, once fully built |
| Undyne | Sustained damage | High - core progression | Rarely |
| Papyrus | Early-mid damage | Medium | A stronger option performs better at similar cost |
| Toriel | Defensive support | Situational | Survivability is no longer the bottleneck |
| Frisk | Starter utility | Low after early game | Main roster improves |
| Flowey | Flex slot | Low | Specialized units become available |
Do not drain your resources upgrading transitional units like Frisk or Flowey to maximum level. Their job is to carry you until your core roster is built, then hand the investment over to Sans, Undyne, or other permanent carries.
Step-by-Step Upgrade Roadmap
Follow this sequence to convert stage rewards into a consistently stronger team without wasting currency.
Stabilize the Opening
Place one reliable unit near the first choke point and add a second only after the opening wave is stable. Keep enough currency in reserve for the next wave instead of spending everything immediately.
Upgrade the Best Position
Improve range or damage on the unit covering the longest section of the path when the next wave becomes difficult. Concentrated upgrades are easier to manage than a wide field of under-leveled units.
Reinvest Clear Rewards
Replay stages when you need extra currency or experience. Upgrade units that consistently contribute during full waves, and test new units in normal content before bringing them into difficult stages.
Apply Traits to Core Units
Once a unit is confirmed as part of your long-term team, use trait rerolls on it. Prioritize damage-focused traits for carries, and range or attack-speed traits when they directly fix a placement or uptime weakness.
Specialize for Hard Content
Build around each difficult stage's specific threats. Use your best-traited units, adjust placement per stage, and stop relying on one universal lineup as content gets harder.
Progression becomes smoother when upgrades are based on actual battle performance instead of rarity alone. Watch which units carry full waves, and those are your investment targets.
Traits and Upgrade Synergy
Traits multiply the value of every upgrade you purchase in a stage. A damage trait on a fully upgraded Sans delivers more total benefit than the same trait on a half-built roster, which is why trait order matters.
| Trait Focus | Combat Benefit | Best Unit Role | Resource Priority |
|---|---|---|---|
| Damage traits | Faster clears, better boss pressure | Main damage dealers | High for permanent carries |
| Range traits | Better coverage, flexible placement | Lane coverage units | High when fixing placement weakness |
| Attack speed | More hits during dense waves | Repeated-attack units | Medium-high |
| Support traits | Consistency, uptime, survivability | Utility units like Toriel | Only after core is stable |
Lock in a useful trait the moment it matches the unit's role, then move to your next priority unit. A carefully chosen reroll target produces a larger team improvement than spreading resources across many incomplete units.
Upgrade Goals Checklist
Essential Upgrade Milestones:
- Stabilize the first three stages with a balanced team
- Fully upgrade one well-positioned core damage unit
- Confirm your long-term roster before spending trait rerolls
- Apply damage or range traits to your primary carry
- Retire transitional upgrades on Frisk and Flowey
FAQ
Q: Should I upgrade many units at once in Undertale Adventures?
No. Concentrating upgrades on one well-positioned unit is easier to manage and usually stronger than a wide field of under-leveled units. Expand only after your core placement is stable through full waves.
Q: Which unit deserves upgrade investment first?
Invest in your permanent carries first - Sans for difficult and boss-focused content, Undyne for reliable general progression. Papyrus is worth upgrading early but should hand off investment once stronger options arrive.
Q: When should I use trait rerolls on upgraded units?
Only after a unit is confirmed as part of your active, long-term team. Use rerolls on core damage dealers first, followed by essential supports. Never spend reroll resources on temporary units you plan to replace.
Q: Do I need to upgrade Toriel if my damage is already strong?
Not necessarily. Toriel's upgrades matter most when survivability or wave pressure is what blocks your clears. If your damage dealers finish waves cleanly, keep investing in them instead.