The Morning After is a band from Essex whose sound has evolved from power metal/metalcore in their earlier days to hard rock, active since 2016. This stylistic journey reflects a versatile approach to heavy music across multiple subgenres.

The Oblyvion is a metalcore band from Mannheim, Germany, formed in 2017. They deliver aggressive metalcore with dynamic arrangements.

The Oracle Machine is a progressive metal band from Hamburg, Germany, formed in 2023 after evolving from metalcore origins. They craft technically ambitious progressive metal compositions.

The Overcome is a metalcore band from Rome, Italy, formed in 2014. They deliver aggressive, breakdown-driven metalcore with modern heaviness and dynamic energy.

The Owl is a melodic death metal/metalcore band from Athens, formed in 2018. Their music combines the melodic guitar harmonies of melodic death metal with the aggressive breakdowns of metalcore.

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The Risen Dread is a groove metal and metalcore band from Dublin, Ireland, formed in 2025. They combine heavy grooves with metalcore aggression and modern heaviness.

The Secret is a blackened crust/grindcore band from Trieste, Italy, active since 2010. They combine black metal darkness with crust punk's raw energy and grindcore's ferocious speed in a genre-defying assault.

Melodic death metal and metalcore band from Tyrol, Austria, The Sky Is Ours were active from 2006 to 2011, operating as an independent act in the regional extreme metal underground. Their music sat at the heavier, riff-driven end of the melodic death/metalcore crossover that characterized much of the mid-2000s European metal scene.