Mental by Nolimit City sits at the darker, more extreme end of the spectrum. Its bonus-buy menu provides several entry points, such as a high-risk option that strips away the feature down to its most volatile core. The asylum theme and shrieking sound effects won’t suit everyone, but the mechanical depth gains respect. For something lighter, Money Train 3 from Relax Gaming offers a hold-and-win bonus round with persistent symbols. The bonus buy here triggers a feature that can link respins into staggering cumulative multipliers, generating genuine suspense with each step.