Stat Rerolls and Stat Locks are the tools that transform a good relic into a great one in Universal Tower Defense Z. While the main stat determines a relic's base quality, the substats provide the optimization that pushes your units from strong to BiS. Stat Rerolls randomize a substat, while Stat Locks protect your best substats from being rerolled. Both resources are limited, making strategic use essential. This guide covers the complete stat reroll system, when to use Stat Locks, substat priority per slot, Stat Reroll economy, and a step-by-step optimization strategy.
How Stat Rerolls and Stat Locks Work
| Tool | What It Does | Source | Weekly Income |
|---|
| Stat Reroll | Randomizes one substat on a relic | Challenges, Raids, Codes | 5-10 |
| Stat Lock | Protects one substat from being rerolled | Raids (rare), Events | 1-3 |
Stat Reroll Mechanics
| Feature | Details |
|---|
| Cost | 1 Stat Reroll per use |
| Result | One substat is randomly replaced |
| Can target specific substats? | No — randomly selects which substat to reroll |
| Can undo? | No — permanent change |
| Stat Lock interaction | Locked substats are excluded from reroll |
The key mechanic is that Stat Rerolls randomly select which substat to change — you cannot target the bad substat directly. This is why Stat Locks are so valuable: they protect your best substats, ensuring the reroll only affects the unwanted ones.
Substat Priority by Relic Slot
Top Slot (HP, Range)
| Substat | Value | Target | Priority |
|---|
| Range | Extends attack coverage | 8%+ | ★★★★★ |
| HP | Survivability | 10%+ | ★★★★ |
| Crit Rate | Burst frequency | 5%+ | ★★★ |
| CD | Faster attacks | -3%+ | ★★★ |
Bottom Slot (CD, Damage, Crit Rate)
| Substat | Value | Target | Priority |
|---|
| CD | Reduces SPA = more attacks | -5%+ | ★★★★★ |
| Damage | Direct DPS increase | 8%+ | ★★★★★ |
| Crit Rate | Burst frequency | 5%+ | ★★★★ |
| Boss DMG | Raid-specific boost | 8%+ (Warlord) | ★★★ |
Accessory Slot (Elemental DMG)
| Substat | Value | Target | Priority |
|---|
| Elemental DMG | Type-specific boost | 8%+ | ★★★★★ |
| CD | Faster attacks | -3%+ | ★★★★ |
| Crit Rate | Burst frequency | 5%+ | ★★★ |
| Damage | General boost | 5%+ | ★★★ |
When to Use Stat Locks — Decision Matrix
Stat Locks are much rarer than Stat Rerolls. Using them on the wrong relic wastes weeks of farming. Follow this decision matrix:
| Relic Quality | Substats | Use Stat Lock? | Action |
|---|
| Good main stat + 3 good substats | CD + Damage + Crit + 1 bad | YES — lock 3, reroll 1 | Highest priority |
| Good main stat + 2 good substats | CD + Crit + 2 bad | YES — lock 2, reroll 2 | High priority |
| Good main stat + 1 good substat | CD + 3 bad | NO — too risky | Reroll without locks, hope for 2+ good |
| Bad main stat | Any | NO — not worth investing | Salvage or use temporarily |
Stat Lock Budget Allocation
| Priority | Unit | Slot | Reason |
|---|
| 1 | Primary DPS (Joyful Captain) | Bottom | CD + Damage + Crit = biggest DPS impact |
| 2 | Primary DPS | Top | Range + HP |
| 3 | Support | Top | HP + Range for buff coverage |
| Never | Farm unit | Any | Fortune set is fine without optimization |
| Never | B-tier units | Any | Will be replaced — do not invest |
Only invest Stat Locks in your permanent S-tier units. Locking substats on a B-tier unit that you will eventually replace is a complete waste of the rare resource.
Step-by-Step Relic Optimization Process
| Step | Action | Resources Used | Target |
|---|
| 1 | Farm relic with correct main stat | None | Get the piece |
| 2 | Check substats | None | Count good substats |
| 3 | If 2+ good substats: use Stat Locks | Stat Locks | Protect best substats |
| 4 | Reroll remaining substats | Stat Rerolls | Improve bad substats |
| 5 | Evaluate result | None | Does it meet targets? |
| 6 | If failed: start over with new relic | None | Get a better base |
Example: Optimizing Fused Warrior Bottom
| Stage | Substats | Action | Resources |
|---|
| Initial drop | CD (-4%), Damage (6%), Crit (3%), HP (2%) | 2 good, 2 bad | — |
| Apply 2 Stat Locks | CD (-4%) ✓, Damage (6%) ✓, Crit (3%), HP (2%) | Lock best 2 | 2 Stat Locks |
| Reroll 1 | CD (-4%) ✓, Damage (6%) ✓, Crit (8%) ✓, HP (2%) | Good roll! | 1 Stat Reroll |
| Reroll 2 (if needed) | CD (-4%) ✓, Damage (6%) ✓, Crit (8%) ✓, Range (5%) | Better! | 1 Stat Reroll |
With 2 Stat Locks and 2 Stat Rerolls, we transformed a mediocre relic into a strong one. The key was using Locks to protect the CD and Damage substats while rerolling the weaker ones.
Stat Reroll Economy
| Resource | Weekly Income | Monthly Income | Primary Source |
|---|
| Stat Rerolls | 5-10 | 20-40 | Challenges + Raids |
| Stat Locks | 1-3 | 4-12 | Raids (rare) + Events |
| Stat Locks from Codes | Varies | Varies | Code rewards |
Stat Rerolls are relatively abundant — you get 5-10 per week from normal farming. Stat Locks are the bottleneck at only 1-3 per week. This makes it critical to use Locks only on high-value relics.
Common Optimization Mistakes
| Mistake | Cost | Correct Approach |
|---|
| Using Stat Locks on C/D tier unit relics | Wastes rare Locks | Only on S/A tier permanent units |
| Rerolling without Locks on 3+ good substats | Risk of losing good stats | Lock first, then reroll |
| Rerolling mediocre relics (1 good substat) | Wastes Rerolls for minimal gain | Get a better base relic first |
| Optimizing Farm unit relics | No meaningful DPS impact | Farm relics are fine un-optimized |
Relic Stat Ranges and Substats
Each relic slot has specific main stat ranges and substat pools. Understanding these ranges helps you evaluate whether a relic is worth keeping or rerolling:
Main Stat Ranges by Slot
| Slot | Possible Main Stats | Min Value | Max Value | Ideal for DPS | Ideal for Support |
|---|
| Top | HP, Range | +500 HP / +2 Range | +5000 HP / +8 Range | Range | HP |
| Bottom | CD, Damage, Crit Rate | -5% CD / +5% DMG / +5% Crit | -15% CD / +25% DMG / +20% Crit | -CD or +DMG | +Crit or +DMG |
| Accessory | Elemental DMG, HP | +5% Ele DMG / +500 HP | +25% Ele DMG / +3000 HP | +Ele DMG | +HP |
Substat Tiers
Each relic can have up to 4 substats. The quality of substats determines the relic's overall value:
| Substat Tier | Example Substats | Value Rating | Keep or Reroll |
|---|
| S | Crit Rate + Crit DMG + Range + CD | ★★★★★ | Keep — extremely rare |
| A | Crit Rate + DMG + any 2 useful stats | ★★★★ | Keep — great relic |
| B | DMG + any 2 useful stats | ★★★ | Keep if main stat is ideal |
| C | 2 useful + 2 useless stats | ★★ | Consider rerolling |
| D | 3-4 useless substats | ★ | Reroll or salvage |
Best-in-Slot (BiS) Relic Analysis
BiS for S-Tier DPS Units
| Unit | Top Slot | Bottom Slot | Accessory Slot | Set Bonus Target |
|---|
| Joyful Captain | Range | CD or Damage | Elemental DMG | Fused Warrior (2pc) |
| Ancient Mage | Range | CD | Elemental DMG | Fused Warrior (2pc) + Warlord (1pc) |
| Pirate King | Range | Damage | Elemental DMG | Warlord (2pc) + Fused Warrior (1pc) |
BiS for Support Units
| Unit | Top Slot | Bottom Slot | Accessory Slot | Set Bonus Target |
|---|
| Support units | HP | Crit Rate | HP | Any defensive set |
BiS for Farm Units
| Unit | Top Slot | Bottom Slot | Accessory Slot | Set Bonus Target |
|---|
| Farm units | HP | Any | Any | No set bonus needed — use any decent relic |
Relic Set Bonus Calculations
| Set | 2-Piece Bonus | 3-Piece Bonus | Total Value | Best Units |
|---|
| Fused Warrior | -5% CD | -7.5% CD + 15% Range | ★★★★★ | All DPS units |
| Warlord | +10% Crit Rate | +15% Crit DMG | ★★★★ | Crit-based DPS |
| Defender | +10% HP | +20% HP | ★★★ | Support and Farm |
| Elementalist | +10% Ele DMG | +15% Ele DMG | ★★★ | Elemental DPS |
Set Bonus vs Individual Stats
| Scenario | Set Bonus Value | Individual Stats Needed | Which is Better |
|---|
| Fused Warrior 3pc | -7.5% CD + 15% Range | Need -10% CD and +15% Range on substats | Set is usually better |
| Warlord 3pc | +15% Crit DMG | Need +20% Crit Rate and +15% Crit DMG | Depends on unit's base crit |
| 2 mixed sets | 2 partial bonuses | Need strong substats to compensate | Substats > partial sets if relics are premium |
Relic Farming and Reroll Strategy
Farming Priority by Difficulty
| Raid Tier | Relic Drop Quality | Shard Drop | Time Per Run | Recommended Runs/Week |
|---|
| Low Tier | Common-Uncommon | Mythic | 5-10 min | 5-7 |
| Mid Tier | Uncommon-Rare | Exclusive | 10-15 min | 3-5 |
| High Tier | Rare-Epic | Secret | 15-25 min | 2-3 |
Stat Reroll Strategy
| Stat Lock | Cost | When to Use | Priority |
|---|
| 1 stat locked | 1 Stat Lock | Lock the most valuable substat | First lock on any relic |
| 2 stats locked | 3 Stat Locks | Lock 2 premium substats | Only on S-tier relics |
| 3 stats locked | 6 Stat Locks | Overkill — usually not worth it | Never on non-BiS relics |
Stat Locks are precious resources. Only use them on relics with an ideal main stat and at least 1 premium substat. Never lock more than 2 stats on any relic — the cost is too high for marginal improvement.
Frequently Asked Questions
How many Stat Rerolls should I spend on one relic?
Up to 10 rerolls if the main stat is good and you have at least 1 locked substat. If you get no improvement after 10 attempts, move to a different relic.
Should I optimize my current relics or farm better ones first?
Farm better main stats first. A Nightmare Raid relic with wrong substats is still better than a Normal Raid relic with perfect substats because the main stat difference is so large.
Can I get Stat Locks from codes?
Occasionally, yes. Check our codes page for any active Stat Lock rewards. These are rare but provide valuable free resources.
Is it worth optimizing relics on A-tier units?
Only after your S-tier primary DPS is fully optimized. A-tier units may be replaced by future S-tier summons, so limit Stat Lock investment to permanent team members. See our tier list for unit rankings.