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Mermaid’s Diamond Slot Review
Play`n Go games3.5/5 · Good
Reviewed by Brett Chatz, Senior Casino Reviewer · Updated June 2026 · 18+Ad disclosure: we may earn a commission when you visit a casino through our links. Commissions never influence rankings or scores — here's how we make money. 18+.
Play Mermaid's Diamond Slot Free Demo
Mermaid's Diamond Slot is a 2017 ocean-themed release from Play'n GO running on a 5x3 grid with 720 ways to win. It pairs an underwater aesthetic with medium-high volatility mechanics, a 96.53% RTP, and a max win of 2,500x your stake. Below the demo, we break down exactly what to expect from this one — the good, the underwhelming, and everything in between.
A Decent Underwater Slot That Won't Blow Your Mind — But Might Surprise You
Mermaid's Diamond sits in a strange middle ground. It's not flashy enough to wow you on first spin, but Play'n GO built enough mechanical depth into the bonus structure that it rewards patience. The mermaid theme is well-worn territory — you've seen the seashells, the treasure chests, the blue-green colour palette a hundred times. What sets this apart is the wild reels feature and a bonus game that actually has some teeth to it. If you want pure spectacle, close the tab and load up Pearls of India. If you want higher volatility ocean action, try Ocean's Treasure by NetEnt. But if you want a medium-high variance 720-ways slot with a solid free spins round and reasonable hit frequency, Mermaid's Diamond still holds up.
How It Actually Plays
The 720 ways-to-win system means there are no traditional paylines. Matching symbols on adjacent reels from left to right pay regardless of vertical position, which gives you more frequent small wins than a typical 20-line slot. In practice, this means your base game isn't a barren wasteland between bonus triggers — you'll see clusters of low-value wins that keep your balance from cratering immediately.
The wild symbol substitutes for everything except scatters and appears on reels 2, 3, and 4. Here's where it gets interesting: wild reels can activate randomly during any spin, turning an entire reel wild. When two or three reels go wild simultaneously, that's where the 2,500x max win becomes theoretically reachable. We say "theoretically" because in our testing, we never hit more than about 800x from a single spin event. The math on that max win requires a perfect storm of wild reels plus premium symbol alignment across all five positions.
A typical session feels like a slow burn. You'll grind through 30-40 spins of modest returns, then a wild reel lands and suddenly a 50-80x win appears. It's medium-high volatility that leans more toward the medium side during base play and ramps up in free spins.
The Bonus Round
Three or more scatter symbols (the diamond) trigger the free spins bonus. Three scatters award 8 free spins, four give you 12, and five scatters deliver 16 free spins. During the bonus round, wild reels become significantly more frequent — this is where the slot's real earning potential lives.
There's also a bonus game triggered by the treasure chest symbol. It's a pick-and-click mechanic where you select items to reveal multiplied prizes. It's not groundbreaking, but it provides a secondary win path outside the free spins.
In our testing, we triggered the free spins bonus roughly every 120-130 spins on average. That's on the slower side for a medium-high volatility slot. When it did hit, payouts ranged from a disappointing 15x (when wild reels didn't cooperate) to a satisfying 430x on our best run. The treasure chest bonus appeared more frequently — roughly every 60-70 spins — but paid considerably less, typically between 5x and 40x.
What 100 Spins Looks Like
- Starting balance: £50 at £0.50/spin (£25 total wagered over 100 spins)
- Base game wins: 38 winning spins out of 100, returning £16.40
- Bonus triggers: 1 free spins round (triggered on spin 87), 1 treasure chest bonus (spin 44)
- Free spins payout: £54.50 (109x stake)
- Treasure chest payout: £8.00 (16x stake)
- End balance: £103.90
- Without the bonuses, we'd have ended at: £41.40 — a slow bleed of about 17% over 100 base game spins
- Biggest single base game win: £6.50 (13x) from a wild reel on spin 63
One session doesn't define a slot, but this pattern — base game erosion saved by bonus rounds — was consistent across our multiple test runs.
Is It Worth Playing?
- Play if: You have a bankroll of at least 200x your bet size and enjoy 720-ways mechanics with moderate bonus frequency. A £100 budget at £0.50 spins gives you reasonable runway.
- Play if: You appreciate wild reel features that can transform dead spins into solid wins without needing a bonus trigger.
- Play if: You want a free spins bonus at a casino to use on a slot with decent RTP (96.53%).
- Skip if: You're chasing life-changing wins. The 2,500x cap is modest by 2024 standards.
- Skip if: You prefer high-frequency bonus triggers. Waiting 120+ spins between free spins rounds tests your patience.
- Skip if: You're working with a bankroll under £40 at minimum bet. The medium-high volatility will eat through thin balances.
How It Compares
| Slot | Volatility | Max Win | Key Difference |
|---|---|---|---|
| Mermaid's Diamond (Play'n GO) | Medium-High | 2,500x | 720 ways, wild reels, pick bonus |
| Mermaids Millions (Microgaming) | Low-Medium | 7,500x | Lower variance, higher max win, classic feel |
| Ocean's Treasure (NetEnt) | Medium | 2,480x | Rising multiplier in free spins |
| Golden Fish Tank (Yggdrasil) | Medium | 1,185x | Player-selected bonus features |
| Reef Raider (NetEnt) | High | 10,000x | Cluster pays, avalanche, much higher ceiling |
Strategy Tips
- Size your bankroll for 250+ spins. With bonus triggers averaging every 120 spins, you need enough runway to reach at least two free spins rounds per session. At £0.20 min bet, that's £50 minimum.
- Don't ignore the treasure chest bonus. It triggers twice as often as free spins and contributes meaningful mid-session recovery to your balance.
- Avoid common casino bonus mistakes — check wagering requirements before using bonus funds on this slot, as some operators weight 720-ways slots differently.
- Play on mobile casinos — this 2017 release was built with HTML5 and runs smoothly on mobile. The 5x3 grid scales well on smaller screens.
- Set a stop-loss at 50% of your session bankroll. If you've burned through half without hitting free spins, the variance gods aren't smiling today. Walk away and try again later.
Where to Play Mermaid's Diamond Slot
Play'n GO titles are widely available across licensed operators. Check our list of best slots sites for trusted platforms carrying this game. UK players should ensure their chosen site holds a valid UKGC licence. If you're looking to try Mermaid's Diamond without risking real money first, look for a no deposit bonus or claim a welcome bonus to extend your session. For quick cashouts after a good run, consider our recommended fast payout casinos.
The Bottom Line
Mermaid's Diamond is a quietly competent slot that rewards the patient grinder more than the thrill-seeker. Its 720-ways system and random wild reels create genuine moments of excitement, and the 96.53% RTP means the house edge is fair. The 2,500x cap won't break any records, but the journey to get there is engaging enough. It's a solid B-tier slot from Play'n GO's back catalogue that still earns its place in rotation.
Key Stats
- Provider: Play'n GO
- RTP: 96.53%
- House Edge: 3.47%
- Volatility: Medium-High
- Max Win: 2,500x
- Reels: 5x3
- Ways to Win: 720
- Bet Range: £0.20 – £100
- Features: Wilds, Free Spins, Scatter Symbols, Wild Reels, Bonus Game
- Release Year: 2017
Responsible Gambling
Gambling should be entertainment, not income. Set time and deposit limits before you play. If you feel your gambling is becoming a problem, visit our responsible gambling page or contact BeGambleAware.org for free support and advice.
Where to play Mermaid’s Diamond Slot
Mermaid’s Diamond Slot FAQ
What is the RTP of Mermaid's Diamond Slot?
Mermaid's Diamond Slot has an RTP of 96.53%, which translates to a house edge of 3.47%. This is slightly above the industry average for online slots and represents fair value for a medium-high volatility game.
How do wild reels work in Mermaid's Diamond?
Wild reels activate randomly during any spin in Mermaid's Diamond. When triggered, an entire reel (reels 2, 3, or 4) turns completely wild, substituting for all symbols except scatters. Multiple reels can turn wild simultaneously, which is how the biggest wins are generated — especially during the free spins bonus round where wild reels appear more frequently.
How often do free spins trigger in Mermaid's Diamond Slot?
Based on our testing, the free spins bonus in Mermaid's Diamond triggers approximately every 120-130 spins on average. You need three or more diamond scatter symbols to activate the round, which awards 8, 12, or 16 free spins depending on whether you land 3, 4, or 5 scatters respectively.
What is the maximum win in Mermaid's Diamond Slot?
The maximum win in Mermaid's Diamond is 2,500x your total stake. Reaching this cap requires multiple wild reels activating simultaneously alongside premium symbol combinations across all five reels. This is most likely to occur during the free spins bonus when wild reel frequency is increased.
Can I play Mermaid's Diamond Slot on mobile?
Yes, Mermaid's Diamond was built using HTML5 technology and is fully compatible with mobile devices. The 5x3 grid format scales well on smartphones and tablets. The game is available at most Play'n GO partner casinos on both iOS and Android browsers without requiring a separate app download.
