Synergies

In short

A synergy switches on while you own at least requiredCount upgrades carrying its tag, and adds its bonus modifiers to your stats. Five exist. Every owned copy counts, so two of the same Charm count twice. Barrel Master cannot be reached with the current items because all Contact items are Gloves.

How it works

1. After every purchase RunState.RecalculateStats calls SynergyResolver.GetActive(Upgrades, synergies).
2. CountTag counts owned upgrades whose tags contain the synergy’s tag (the run’s list, so duplicate Charms count once each, and the batter’s starting kit counts).
3. Each active synergy’s bonus modifiers are added after the batter, level perks and upgrades. They stack like any other modifier. See Upgrades and Synergies and Stats System.
4. The description is generated: "<count>+ \"<tag>\" items", e.g. 3+ "Power" items.

Numbers

id	Name	Tag	Needs	Bonus
slugger	Slugger	Power	3	+50% HR Multiplier
clockwork	Clockwork	Timing	2	+20% Timing Window
barrel_master	Barrel Master	Contact	2	+20% Contact
high_roller	High Roller	Greed	2	+2 Coins per HR (flat)
in_the_zone	In the Zone	Green	2	+0.5 Green HR Score (flat, +50%)

Which items carry each tag, and how to reach it

Tag	Items (slot)	Reachable?
Power	Maple Bat, Corked Bat, Titanium Bat (Bat); Pine Tar Grip (Glove); Spiked Cleats (Cleats)	Yes, only as one Power bat + Pine Tar Grip + Spiked Cleats (one item per slot, no Power charm)
Timing	Batting Gloves (Glove); Pocket Metronome (Charm, locked at first)	Yes: Gloves + Metronome, or two Metronomes
Contact	Sweet Spot Tape, Pine Tar Grip, Sweet Spot Sticker (all Glove)	No: only one Glove can be held
Greed	Lucky Penny, Reroll Coupon (both Charm)	Yes: any two, including two of the same
Green	Green Light, Hot Streak Wristband (Charm); Sweet Spot Sticker (Glove)	Yes
Risky, Lift, Endurance, Style	various	No synergy uses these tags

In the code

File	What it does
Assets/_Project/Scripts/Data/DefaultContent.cs	Synergy(id, name, tag, count, bonus...)
Assets/_Project/Scripts/Data/SynergyDefinition.cs	Fields: tag, requiredCount (default 2), bonus
Assets/_Project/Scripts/Upgrades/SynergyResolver.cs	CountTag, GetActive
Assets/_Project/Scripts/Run/RunState.cs	RecalculateStats adds active synergy bonuses; ActiveSynergies

Gotchas

• Barrel Master is still dead content at 45a2167: all three Contact items share the Glove slot, and buying a Glove replaces the one you hold. A Contact Charm, Bat or Cleats item would make it reachable.
• Tags are matched as exact, case-sensitive strings.
• A synergy turns off again if a slot replacement drops your count below the requirement (e.g. swapping the Corked Bat for the Launch Pad Bat, which is tagged Lift).
• Synergy bonuses only exist inside a run; the batting cage uses the batter’s stats, level perks and starting kit only.

Related

• Upgrades: every item and its tags
• Upgrades and Synergies: the rules
• Stats: what the bonuses change
• Add a Synergy