How to Get Gems in 8 Bit Tower Defense (and What to Spend Them On)

Quick answer

You earn Gems in 8 Bit Tower Defense by claiming Index rewards for newly discovered units, completing Quests and achievements, claiming the one-time Roblox group bonus in Settings, and redeeming codes. Gems are spent mainly on unit summons — a SUMMON x10 costs 500 Gems — and can also pay for rerolling a unit's stat grades.

• Index: Gems for each newly discovered unit, collectable with CLAIM ALL
• Quests menu: achievement rewards observed at 250-2,000 diamonds each
• Settings: like the game and join the Roblox group for a one-time +100 Gems and +1 Trait Reroll
• Codes: redeemed in Settings, several have awarded Gems

Gems are 8 Bit Tower Defense's hub currency for getting new units. The HUD shows them as blue diamonds alongside Gold, Dice/Trait Reroll tokens and event Candy — for example, one player sat at 1,830 Gems while deciding what to pull. Unlike Gold, which funds what you place and upgrade inside a match, Gems are what you take back to the hub to summon more units with.

How to get Gems

Claim Index rewards after every summoning session

The Index tracks every unit you discover for the first time, and each new discovery builds toward a Gem payout. On one player's Index screen, those payouts showed up as +375 gems for 13 discoveries, +360 gems for 5 discoveries and +240 gems for 4 discoveries, all collectable through a CLAIM ALL button.

The practical habit here: open the Index whenever you finish a batch of summons and press CLAIM ALL so the rewards for your new discoveries reach your balance.

Work through Quests and achievements

The Quests menu spans levels, achievements, titles and event tabs, and pays out diamond rewards — the same blue-diamond Gem currency shown in the HUD. Achievements observed in gameplay paid between 250 and 2,000 diamonds each, and one player narrated claiming achievements and immediately receiving more gems. Exact quest payout values vary, so treat the Quests menu as a steady background source: check it after playing, see what's completed, and claim. Progression-adjacent quests tie directly into how you level up, so playing normally keeps this source running.

Take the one-time group reward

In Settings, right next to the CODES field, there is a "Join the Roblox group - Like the game and join the group for free gems!" offer with a CLAIM button. Once you have liked the game and joined the official Roblox group, claiming pays +100 Gems and +1 Trait Reroll.

Two things to know: this is a one-time claim, not a repeatable source, and it is separate from redeeming codes — it sits beside the code field but works independently. If you haven't claimed it yet, it pays +100 Gems and +1 Trait Reroll once you've liked the game and joined the group. The group reward page covers the offer in detail.

Redeem codes for a Gem lump sum

Codes redeemed in Settings have awarded Gems alongside Gold, Trait Rerolls, Stat Rerolls and event Candy — several of the game's codes to date have been Gem codes. Codes are one-time per account and can expire, so redeem them while they work. The maintained list of active codes and their exact rewards lives on the Codes page.

What Gems are spent on

Unit summons — the main sink

Gems pay for unit summons in the Summon menu, where a SUMMON x10 ten-pull costs 500 Gems. The posted rates for the standard pool are Rare 70.74%, Epic 26%, Legendary 3%, Mythic 0.25% and Secret 0.01%. Event banners add limited exclusives on top of that pool — during the Hollow Night event, for example, the Headless Horseman was available as a 0.02% Secret and the Grim Reaper as a 0.5% Mythic. Banner lineups change with events, so the rates you see on screen are the ones that count.

The game points you at summoning from the very start — the tutorial's first steps tell you your squad needs more units and to open SUMMON to call some in. What you pull feeds directly into building your team, so it's worth knowing which pulls matter before you spend — the units list and tier list help you judge a banner.

Stat grade rerolls — the alternative payment

On a unit's Stats sub-tab, the REROLL GRADES button can be paid for with either Stat Rerolls or Gems — observed on the Chameleon screen as "REROLL GRADES - 45 Stat Rerolls (or Gems)". The exact Gem price wasn't displayed on that screen, but Gems are an accepted payment when you're out of Stat Rerolls.

One warning before you reroll: rerolling grades empties the unit's Potential counter — the screen states "Rerolling empties it" outright. If you've been building up Potential on a unit, weigh that against the reroll. This ties into the wider reroll economy covered on the stat rerolls and trait rerolls pages.

Summons and Gems feed each other

The two halves of this page connect: new discoveries from summons feed straight into the Index and its Gem payouts. Every 500-Gem ten-pull has a chance to surface units you've never owned before, and each of those discoveries becomes a claimable Index reward — so early on, summoning partially refunds itself through the Index.

That makes the early-game loop simple: claim the group reward and codes, summon in ten-pulls, claim all new Index discoveries, then put the returning Gems back into more summons until your roster covers the pool. Once most pulls stop producing new discoveries, the Index refund slows down, and Gems shift toward event banners and stat grade rerolls instead. For how this fits into the wider economy, see the currencies guide and the progression guide.