This guide aims to tell you which mods to use for your heirlooms.

An important thing to remember with heirlooms is that Drop Rate mods do not scale with seconds of production loot (Jestimp / Chronoimp / Map Cache / Bone Shrine), whereas Efficiency mods do. Therefore, starting from Epic heirlooms, Efficiency mods for Food, Wood and Metal are the obvious choice against Drop Rate mods.

Once you unlock Plagued heirlooms, keep two shields, one with VMDC/Attack/Crit/Crit/PB - for regular farming, and one with Attack/Crit/Crit/PB/Health - for Spires, C²'s and pushing.


Plaguebringer and Fluffy Exp are unlocked starting with Plagued heirlooms at zone 500.

Generally the easiest thing to do is check with the following player-made calculators:
https://swaqvalley.com/td_calc/
https://spiredb.tdb.fi/
(Note: the calculators may be outdated and missing certain endgame upgrades)

If you have a 2 mod core, keep a fire damage core with Runestone Drop Rate and Fire Trap Damage.
If you have a 3 mod core, keep a poison damage core with Condenser Effect, Runestone Drop Rate, and either Poison Trap Damage or Lightning Trap Power
Once you have 4 mod cores, keep two cores:

Fire Core:
• Fire Trap Damage
• Strength Tower Effect
• Runestone Drop Rate
• Lightning Trap Power

Poison Core:
• Condenser Effect
• Poison Trap Damage
• Runestone Drop Rate
• Lightning Trap Power

Depending on your Fire Trap/Poison Trap upgrades, the relevant damage type will usually be much stronger than the other, so keep a look out and apply the right core accordingly to boost the stronger damage type.
The final core will be Fire Core, after acquiring all Spire TD upgrades.

Best U2 Staff has the following mods:

• Pet Exp
  
• Farmer Efficiency
  
• Lumberjack Efficiency
  
• Miner Efficiency
  
• Explorer Efficiency / Fragment Drop Rate
  
• Dragimp Efficiency
  
• Parity Power (unlocked with Enigmatic)

At different stages of the game you may need different mods more (e.g. Miner Efficiency > Farmer Efficiency early on in U2, but once you unlock Greed, you need both).

For fragments, Fragment Drop Rate is better once you have Greed, then Explorer Efficiency is better once you have a lot of Runetrinkets.

Also keep:

• A staff with maxed Scientist Efficiency for Microchip farming
  
• A staff with Scientist Efficiency + Farmer Efficiency + Miner Efficiency + other good mods, for Archaeology

There are plenty of shield combinations to keep for different purposes. Here's a list of the generally useful ones.

Keep all these shields even if you're past their described "purpose", they can and will be needed for other things in the future, whether it's for content that hasn't been released yet or content that is too new to have been properly analysed.

All optimal Radiating shields have Trimp Attack and Crit Damage on them. The other 4 mods vary:

• VMDC / Crit Chance / Trimp Health / Gamma Burst - Early Buble/Early Archaeology
  
• VMDC / Crit Chance / Trimp Health / Prismatic Shield - Late Buble/Melt
  
• VMDC / Plaguebringer / Crit Chance / Gamma Burst - U1 C²/Daily
  
• Plaguebringer / Trimp Health / Gamma Burst / Prismatic Shield - Duel
  
• Plaguebringer / Crit Chance / Trimp Health / Prismatic Shield - Push
  
• Plaguebringer / Crit Chance / Trimp Health / Gamma Burst - Trapper/Trappapalooza
  
• Crit Chance / Trimp Health / Gamma Burst / Prismatic Shield - Shielded achievements

All optimal Hazardous shields have Trimp Attack, Trimp Health and Crit Chance on them. The other 3 mods vary:

• VMDC / Prismatic Shield / Plaguebringer or Crit Damage - Radon
  
• VMDC / Plaguebringer / Crit Damage - U1
  
• Plaguebringer / Prismatic Shield / Crit Damage - Push

All optimal Enigmatic shields have Trimp Attack, Trimp Health, Crit Chance and Crit Damage on them. The other 3 mods vary:

• VMDC / Inequality / Prismatic Shield - Radon
  
• VMDC / Breed Speed / Plaguebringer - U1
  
• Plaguebringer / Inequality / Prismatic Shield - Push