Perhaps cold-based weapons, generally short ranged but also available in grenade launcher ammo format as well as negative energy lasers would be examples of weapons that can cause slow status effects.
However this weapon would probably work contrary to Overload status.
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Grappling would more likely produce a 'PINNED' status effect though it would result in both Mechas being sitting ducks for the duration of the pinning, and only small scale weapons, mainly integral, being able to fire.