So ancient fervour is describe as below. But what are the corresponding accord and elemental ? it doesn't really say. Is frost Abanazaar ? what is it ? cannot see.

Also are we talking only about spells or also attacks ? Because in one hand it talks about "skills" in general and after it talks about spells. Will a missile attack such as Phantom blade with the frost addon works ?

Also I want to point out that using "certain skills"in your choice of words to describe a passive trigger is really bad . It doesn't say anything about what skills. I have seen it many time and only makes things more confusing (og. Omnitempest passive description)
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Ancient Fervour is part of the Oracle of the Trinity branch.

Unlocking this Passive Skill provides the following bonuses:

Using certain elemental skills grants you their corresponding "Accord".
Each Accord has different effects depending on its base element.

"Beelmalik's Accord" increases your critical hit chance for a few seconds.
"Abanazaar's Accord" increases your damage for a few seconds.
"Etheliel's Accord" increases your chance to inflict ailments for a few seconds.

Spells that inflict fire, frost, or lightning ailments grant passive bonuses called "Accords". Up to 1 "Accord(s)" can be active concurrently. Triggered "Accords'. remain locked for 1s.
"'Abanazaar's Accord" is active for 5.0s unless it is triggered again. You have 20% Damage when "Abanazaar's Accord" is active
"Etheliel's Accord" is active for 5.0s unless it is triggered again. You have 50% Ailment Chance when "Etheliel's Accord" is active.
"Beelmalik's Accord" is active for 5.0s unless it is triggered again. You have 50% Critical Chance when "Beelmalik's Accord" is active.