The other guy gave a bit of misinformation...

1: Do not use it against Mask Change, as they can then chain that searched Mask Change, and they will not have it in their hand during resolution.

Heroes: Calling Bubbleman is good (if they set/play cards from their hand so that there is only one left, this is sometimes a tell that they are going to summon Bubbleman).

2: Calling the mirrors is about the worst thing you can do, next to calling a card on the Forbidden List. The spells can banish themselves from the graveyard to search another spell.

Nekroz: The best time is to use it in response to the activation of one of the ritual spells. If they use Kaleidoscope, Unicore is more than likely in their hand. If you chain the Mind Crush to Kaleidoscope calling Unicore, they will be forced to discard their Unicore before Kaleidoscope resolves. This can force them into awkward plays where they have to summon a monster they didn't want to, and tribute monsters they didn't want to (or summon nothing at all). If they do a lot of searching and you can tell which Nekroz they are going to summon off of the other spells, calling that with Mind Crush is also good. With Cycle, calling Shurit is usually a safe play (unless they are summoning Clausolas with Djinn). Some players are now setting their Shurit before activating Cycle/Mirror if they do not need their normal summon to play around Mind Crush.

Shaddolls: Most Shaddoll decks now include Star Seraphs. Chaining Mind Crush to the activation of Sovereignty from hand will stop them from plussing from the combo. Calling Shaddoll Fusion is also good if you know it is in their hand, or if you have an Extra Deck monster on the field and you can afford to risk the blind Mind Crush. You can also chain it to the activation of their fusions if you know one of their monsters in hand (if it's a Shaddoll monster it will get its effect, but it can force them to be unable to resolve the fusion). In general, it is not that strong against Shaddolls.

BA: You can use it against the searched Tour Guide. You can use it in response to their effects to special summon themselves from their hand (this will make the graveyard effect unable to activate because they already activated the effect to special summon it from the hand.)

Qlis: Using it on a searched Scout is usually the best. In general, you should know some of the cards in your opponent's hand, so just use it when it will have an impact.

The others are mostly just calling searched cards (dunno much about Frightfur/Ghostricks).