What spellcasting ability is used for the Githzerai race's version of the Detect Thoughts spell?

Question

The Detect Thoughts spell states:

[...] the creature can use its action on its turn to make an Intelligence check contested by your Intelligence check if it succeeds, the spell ends.

This spell is given to the Githzerai race in MToF pg. 96 at 5th level. It is listed as using Wisdom as the spellcasting ability.

When you reach 5th level, you can cast the detect thoughts spell once with this trait [...] Wisdom is your spellcasting ability for these spells.

Does this spell still need the check made by the Githzerai to be Intelligence?

I assume it would.

Answer 1

Intelligence is always used for this Detect Thoughts check

As you note, the description of the spell specifies that an Intelligence check is needed. This is independent of the caster's spellcasting ability. Compare to something like Dispel Magic which states (emphasis mine):

For each spell of 4th level or higher on the target, make an ability check using your spellcasting ability.

Dispel Magic uses the caster's spellcasting ability but Detect Thoughts has no such wording, calling for an Intelligence check specifically so that's what needs to be done.

If you are curious as to why a spellcasting ability is relevant, note that it is still used to calculate the spell's save DC as usual. (see this related question on that).

Also note that Detect Thoughts can also be used by bards, sorcerers and Great Old One warlocks¹, all of which use Charisma as a spellcasting ability. This particular check of the Detect Thoughts spell is always made with Intelligence regardless.

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^{1. Noted by NathanS}