Is it really a good idea to make monsters unmovable? Including bosses

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SuperMotte wrote:

It doesn't state if reduced or less but if it is reduced... our enemies (including bosses) have 100% reduced movement speed -> they can't move at all.

Temporal Chains does not have any modifier to movement speed. It has a global slowing effect that applies at an entirely different level and cannot stack additively with modifiers to actual movement speed because it's applying to a different thing. This is why it uses different language.
It doesn't matter whether it's "reduced" or "less" in this case since that only matters for things modifying the same value. Technically it is a less modifier, which matters in terms of how it stacks with other "slow" effects (i.e. Chill).