How to Upgrade Units During Battle in 8 Bit Tower Defense (and What Upgrades Do)

Quick answer

Tap one of your own units on the battlefield, then press UPGRADE. In-match upgrades are paid with the cash shown in the battle HUD — cash your units earn from every enemy they defeat during that match — and each upgrade improves that placed unit's combat stats.

• Upgrades belong to the unit you tapped: the observed upgrades changed that unit's own combat stats.
• The upgrade panel shows the price and the effect of the next upgrade before you pay.
• This is separate from the hub's Gold-based LEVEL UP system, which raises your units between matches.

Upgrading units mid-match is one of the two core ways your defense gets stronger in 8 Bit Tower Defense, alongside placing more units. The game's own tutorial teaches it during the training match: 'Every defeat pays cash. Tap one of your units, then press UPGRADE.'

How to upgrade a unit you have already placed

1. Have a unit on the field. If you are still working through placement, the unit placement guide covers picking a unit from the bottom bar and tapping a lit spot beside the road.
2. Build up match cash. Every enemy your units defeat pays cash, and matches also start you off with some — recorded matches began with $1,000 in one Wave 0/8 match and $1,614 in an Act 2 restart.
3. Tap one of your own placed units.
4. Press UPGRADE in the panel that opens and pay the cash price shown.

Placements and upgrades draw on the same in-match cash pool, so every upgrade is a choice between strengthening an existing unit and putting another one on the field.

What an upgrade costs

Prices are shown on the upgrade panel before you commit, and they vary by unit and by upgrade tier. Next-upgrade labels observed in recorded matches included 42, 600, 952 and 2,000 cash — treat those as examples of the range, not a fixed price table. The recorded players also ran into this directly: one unit drew the comment 'this guy is so expensive for some reason', while another upgrade was welcomed as 'only 600'.

If a unit's next upgrade costs more than your current cash, the practical alternative is to keep defending — each defeated enemy adds more cash — or spend the same money on an additional placement instead.

What an upgrade does

Upgrading changes that unit's combat stats, and the panel advertises what the next upgrade does before you buy it. Effects observed in recorded matches include:

• One unit's next upgrade was advertised as doubling its damage.
• A King upgrade read 'Plus 60 damage. Slows by 30%.'
• Upgrading a Scout slime improved its spawn interval from every 10 seconds to every 9 seconds, with 57 damage shown.
• Upgrading one long-range unit enlarged its attack circle ('So you can upgrade it. Now it's larger.').

Each of these was observed on one specific unit in one match, and the same upgrade does not necessarily grant the same effect on other units. Because the next upgrade's effect is written on the panel, the reliable habit is to read the label for the exact unit you are about to pay for rather than expecting a fixed bonus.

Upgrade tiers are visible on the field, and units can be sold

You can see how far a unit has been upgraded at a glance: upgraded units display a larger level number marker on the field. Placed units can also be sold back for cash during the match — one unit showed a sell value of 840 — which lets you recoup part of your investment and put the cash somewhere else; the selling units page covers that in detail.

Battle upgrades vs. leveling up in the hub

In-match upgrading is easy to confuse with the game's other upgrade system, but they run on different currencies and different screens:

The tutorial points you to the hub side with 'Gold from battles levels up your units' and 'Press LEVEL UP. Each level adds damage. Squad units also gain XP from every match.'

According to ProGameGuides, Gold lets you level units up to level 100, increasing your unit's damage output each time you upgrade it during battle, and you can also feed units of lesser rarity to your main unit to raise its level without spending Gold. The leveling up guide walks through that system, and the gold guide covers earning the currency that funds it.

Mythic evolution is a separate system again

The official game description lists one more progression — 'Evolve Mythics into stronger forms' — separately from 'Place your units, upgrade them, unleash their abilities'. Evolution applies to Mythic units and happens outside the match upgrade button; if you are looking for it, the Mythic evolution guide covers that procedure.

For how these upgrades fit into a whole match plan — where to place, what to buy first and how to hold the road — see the defense strategy guide.