Hi everyone,

One of my players has casted Mind Spikes on a invisible creature, failing the saving throw they could tell the invisible target's location while maintaining concentration. The same player now want to use Maximilian’s Earthen Grasp on the invisible target.

I see two problems on this first when they start casting the second spell they lose concentration on the first one and they don't know anymore the location of the target. Second Maximilian’s Earthen Grasp says that you must see the target while Mind Spike says that you know the location only.

What are your thoughts on this? Thank you.

First of all, they shouldn't have been able to cast mind spike on an invisible creature, since that spell also specifies that you need to see the target.

But apart from that, mind spike says:

While you have this knowledge, the target can’t become hidden from you, and if it’s invisible it gains no benefit from that condition against you.

Very strictly speaking this is still a bit vague, but if we interpret it with a certain benefit of the doubt, I think we could agree that this means that the caster of mind spike can treat the target as if they were not invisible.

And yes, as soon as they start casting maximilian’s earthen grasp, they lose concentration on the previous spell, but I'd argue that the target only needs to be viable exactly up to this point.

You only need to fulfill the targeting condition when casting the spell, not to continue concentrating on it.

First off, Mind Soike also requires you to see the target so was the target visible when they cast it?

Second, you are correct that they lose concentration to cast another concentration spell. 

In either case it doesn’t matter since they can’t see it

Thanks for the answers it was my fault not to give more details :)

The target of Mind Spike has failed the saving throw before becoming invisible so once invisible the player is still aware of the location of the target. So at this point the main question is can the player cast Maximilian’s Earthen Grasp swapping concentration or when they cast the second spell they can't target the enemy because they lose concentration on Mind Spike and so they don't know anymore where the target is?

In my opinion, the spell can only be started to cast if the target is valid and the target only becomes invalid (since concentration was dropped) after the new spell has started to be cast. So in my opinion, this is doable.

Context from Sage Advice:
https://www.dndbeyond.com/sources/sac/sage-advice-compendium#SA264

If I’m concentrating on a spell and I cast another spell that requires concentration, when does my concentration on the first spell end?

If you’re concentrating on a spell, your concentration on it ends immediately when you start casting another spell that requires concentration.

If you lose concentration when you start casting another concentration spell then the target now has the benefits of the condition and although you can cast MEG in an adjacent square the hand cannot attack the target because you cannot see them. MS’s effect is not there for you to ignore the invisible conditions to attack with MEG, imo.