Originally Posted by Ussnorway
anyone else casting spells at that enermy may find the hex usful if their spell requires a check for example Gale casts Melf's Acid Arrow and hex makes the enermy less chance to make its save for 1/2 damage
Unfortunately, this is not how hex works.
Originally Posted by mrfuji3
Hex applies debuffs to ability checks, not saving throws. It should not affect enemies' abilities to fail your saving throws.
Originally Posted by Kethlar
From the D&D 5e ruleset:
[...]

You place a curse on a creature that you can see within range. Until the spell ends, you deal an extra 1d6 necrotic damage to the target whenever you hit it with an attack. Also, choose one ability when you cast the spell. The target has disadvantage on ability checks made with the chosen ability.
I.e., the enemy would make Perception checks to notice your stealthed characters at disadvantage.
Enemies make Saving Throws, not ability checks, to save for 1/2 damage against spells including Melf's Acid Arrow.