Using Avatars for elemental testing.

This guide is by minimusdecimus. 
General assumption:
Playing summoner it becomes obvious that all terrestrial avatars have a magic-evasion potency bordering on immunity to spells/abilities of their element and the element they are ascendant. For example Ifrit is fire, fire is ascendant to ice; Ifrit has high fire and ice evasion, but low water evasion. Their seemingly infinite magic-evasion allows them to shrug off corresponding enfeebs that would cripple a party, or spell damage that would kill a normal player.
Typically, Avatars display a 1/8 resist-rate to corresponding elemental damage; taking only 12.5% of the full damage (or in other words, reducing spell damage by 87.5%).* They are also functionally immune to elemental enfeebles. 
With this knowledge, Avatars can be used to discern the elemental affinity of different attacks, and testing has verified that: 
* Qiqirn - Kibosh (amnesia) fire-based, confirmed with Leviathan, Ifrit
* Imp - Abrasive Tantra (amnesia) fire-based confirmed with Leviathan, Ifrit
* Bat-Trio - Sonic Boom (attack down) is water-based, confirmed with Ramuh, Leviathan (Since bat-trio only have two TP abilities, this makes ramuh and leviathan ideal choice when fighting bats as both are immune to Sonic Boom, and have high native -pdt to deal with Jet Stream) 
* Giant Bat - Ultrasonics (aoe evasion -25) is ice-based, confirmed with Ifrit,Shiva
* Euruka - Incinerate is fire damage, confirmed with leviathan/Ifrit.
* Manticore - Riddle is non-elemental Max MP Down.  Riddle landed 100% of the time on all avatars
* Tonberry - Mijin Gakure is non-elemental Magic Damage, not fire damage. Ifrit/Leviathan take exactly the same damage as any other avatar.          
   
Oddities/not fully tested:
* Mimic's Death Trap (aoe poison, stun) is thunder-based, Ramuh takes reduced damage and immune to stun. Titan however takes typical damage and gets stunned. 
* Magic Pots - Mind Drain is earth or thunder (shouldn't be?), Titan evades 99,9%. 
* Diabolos has some level of resist-light and/or resist-sleep(light) vs Yawn
* Carbuncle doesn't appear to have ANY resist-sleep or resist-light trait vs sleep (Light/Dark
    *1 - While testing Incinerate, it appears leviathan/ifrit have the same quantity of fire-evasion and/or -MDT; both took 39dmg from the same incinerate. In another example, leviathan received 97dmg, carbuncle 775; and 87.5% reduction or 1/8th resist.