Sorry new here but I had a question:

We have a sorcerer who is using the new cantrip Mind Sliver.  He wanted to use the Cantrip then Quicken a Hold Person spell to get the benefit of the d4 reduction.

From what I have read this is acceptable but I wanted to get the consensus here. 

Yes it works. Mind sliver works on next saving throw before end of next turn. This would be the next saving throw. 

It works. A bit like a poor man's heightened spell. 

Yeah, that works.

Works.

And this is brutal if a Shadow Sorc using a Hound of Ill Omen. With disadvantage to their saves and -1d4 penalty as well - you can easily lock the enemy out while the mind sliver and your hound damages them (hound even getting auto-crits). 

Even better if the party has another spellcaster able to cast Bane on the same target. They'll have almost no chance of getting free from the Hold.

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.

Thanks all!

Quote from temery2383 >>

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.

 This is very important! 

I’m confused, how are you allowed to break the rule on spellcasting? Am I missing something? If a spell is cast, even a cantrip, you can only cast a cantrip during your bonus action.

so you can cast Mind Sliver as your second spell, thus you have to wait until your next turn for the effect. Or you can cast Mind Sliver and then cast a cantrip that subjects the target to a saving throw which kinda wastes the effect. But I don’t see how you can cast Mind Sliver and say Fireball on the same turn

Quote from CynnamonV >>

I’m confused, how are you allowed to break the rule on spellcasting? Am I missing something? If a spell is cast, even a cantrip, you can only cast a cantrip during your bonus action.

so you can cast Mind Sliver as your second spell, thus you have to wait until your next turn for the effect. Or you can cast Mind Sliver and then cast a cantrip that subjects the target to a saving throw which kinda wastes the effect. But I don’t see how you can cast Mind Sliver and say Fireball on the same turn

 You've hot it the other way around. If you cast a spell as a bonus action the only spell you can cast as an action is a cantrip.

So you can cast mind sliver (a cantrip) with your action, then quicken any spell as a bonus action.

Quote from DxJxC >>

Quote from CynnamonV >>

I’m confused, how are you allowed to break the rule on spellcasting? Am I missing something? If a spell is cast, even a cantrip, you can only cast a cantrip during your bonus action.

so you can cast Mind Sliver as your second spell, thus you have to wait until your next turn for the effect. Or you can cast Mind Sliver and then cast a cantrip that subjects the target to a saving throw which kinda wastes the effect. But I don’t see how you can cast Mind Sliver and say Fireball on the same turn

 You've hot it the other way around. If you cast a spell as a bonus action the only spell you can cast as an action is a cantrip.

So you can cast mind sliver (a cantrip) with your action, then quicken any spell as a bonus action.

 I thought it applied both ways, or specifically retroactively. So even in the proposed order, you’d have to cast a cantrip as a bonus action

Quote from CynnamonV >>

Quote from DxJxC >>

Quote from CynnamonV >>

I’m confused, how are you allowed to break the rule on spellcasting? Am I missing something? If a spell is cast, even a cantrip, you can only cast a cantrip during your bonus action.

so you can cast Mind Sliver as your second spell, thus you have to wait until your next turn for the effect. Or you can cast Mind Sliver and then cast a cantrip that subjects the target to a saving throw which kinda wastes the effect. But I don’t see how you can cast Mind Sliver and say Fireball on the same turn

 You've hot it the other way around. If you cast a spell as a bonus action the only spell you can cast as an action is a cantrip.

So you can cast mind sliver (a cantrip) with your action, then quicken any spell as a bonus action.

 I thought it applied both ways, or specifically retroactively. So even in the proposed order, you’d have to cast a cantrip as a bonus action

 Nope. It does apply retroactively, but different than that. If you cast a leveled spell with your action you can't even cast a cantrip with your bonus action.

You can use your bonus action after your action or before it. It's entirely your choice (there are few exceptions but none that concern spellcasting).

The rule is if you cast a spell, of any level, as a bonus action then all other spells you cast that turn must be cantrips.

So, if you first cast a levelled spell as your action, you cannot then cast any spell as a bonus action since it would violate the above rule. But if you cast a cantrip as your action, you're free to cast a spell, of any level, as your bonus action.

This means that yes, casting the cantrip Mind Sliver for your action and following with Hold Person/Monster as your bonus action after it, is perfectly valid.

Quote from Cyb3rM1nd >>

You can use your bonus action after your action or before it. It's entirely your choice (there are few exceptions but none that concern spellcasting).

The rule is if you cast a spell, of any level, as a bonus action then all other spells you cast that turn must be cantrips.

So, if you first cast a levelled spell as your action, you cannot then cast any spell as a bonus action since it would violate the above rule. But if you cast a cantrip as your action, you're free to cast a spell, of any level, as your bonus action.

This means that yes, casting the cantrip Mind Sliver for your action and following with Hold Person/Monster as your bonus action after it, is perfectly valid.

 Ok thanks!

Quote from Cyb3rM1nd >>

You can use your bonus action after your action or before it. It's entirely your choice (there are few exceptions but none that concern spellcasting).

The rule is if you cast a spell, of any level, as a bonus action then all other spells you cast that turn must be cantrips.

So, if you first cast a levelled spell as your action, you cannot then cast any spell as a bonus action since it would violate the above rule. But if you cast a cantrip as your action, you're free to cast a spell, of any level, as your bonus action.

This means that yes, casting the cantrip Mind Sliver for your action and following with Hold Person/Monster as your bonus action after it, is perfectly valid.

 The best explanation of one of the most misunderstood rules of 5e. Thank you.