Does Mind Sliver Stack?
Yes It Does. the Effects of Different Spells Add Together While the Durations of Those Spells Overlap. This Rule Goes on to Impose Stacking Restrictions on...
Is mind sliver any good?
Mind Sliver works best as a combination 1-2 punch with another caster. The damage is not really the central feature of this spell. Instead, it's the debuff to the target's next saving throw that really shines. This one is great to throw immediately before a party member can drop a big save-or-suck spell of ability.
Is mind sliver a bonus action?
Yep, it works. Just make sure that you cast mind sliver as your action and then quicken hold person as your bonus action. If you quicken mind sliver as your bonus action instead, you can only cast a cantrip as your action.