First, I need to explain that in LoT2, the enemies' have separate debuff resistances. For example, 9F Tenshi has 0 Debuff-resistance to DEF and MND. This means she can be debuffed in Defense and Mind quite easily even with someone with weak Debuff. Tenshi also has a Debuff-resistance of 60 in ATK and MAG so you need stronger debuff for it to proc. I don't know how strong it is needed, though.
Lastly, Tenshi has Debuff-resistance of 100 in Speed so it is nearly impossible to debuff her Speed without someone with 100% or more Debuff chance. Note that even with 100%, it is still hard to proc so you need more than that for it to land reliably. You can use Reisen's Intense Vertigo or Sheer Force/Arm-Twisting skill to lower the resistances.
Kogasa has a fixed 100% Debuff chance in her Dark attack so she can almost always land a debuff even on the most resistant enemies. Other characters with a fixed 100% Debuff chance are Kasen, Utsuho, Alice, Eirin, Reisen, Iku, Kanako and Eiki. Hexer's subclass spell also has a fixed 100% chance. However, Hina and Suwako (her CLD spell only) are the only ones with 100% chance who can increase the Debuff chance further through leveling up their spell.
Also, the debuff resistance listed in Keine's bestiary is for Attack-Debuff only.
And also, Marisa's underwhelming Master Spark is the reason why I put her in "Team Unappreciated."