Trial-Size Trial by Ice

These guides are a recollection of my level 20 cap avatar fights, presented in the order I cleared them in. Since I will be using a similar format for each guide, you might wish to read one and skip the others to avoid similar content.

History
Round 1 - Titan. I quickly learned "Astral Flow" dropped my MP to ZERO upon use and lost the fight after failing to resummon Carbuncle in time.

Round 2 - Ramuh. Although I brought and used Yagudo Drinks this time around, I still was not recovering MP fast enough and failed to resummon Carbuncle yet again. As such, I decided to synthesize some Ethers on Secret mule before my next attempt.

Round 3 - Shiva. Everything was going well until Shiva used "Diamond Dust" just after I had resummoned Carbuncle. Since I took a hit prior to "Diamond Dust," Shiva managed to one-shot me using her special ability.

Round 4 - Ifrit. Bewildered, I vowed for vengeance and tackled my fourth avatar. After working out my previous flaws, I finally managed to win a fight. This battle greatly boosted my morale and would become the basis for all future victories.

Preparation
I suggest the following for each avatar fight:

• 1 to 2 Yagudo Drinks
• 2 to 3 Ethers
• 5 to 10 Hi-Potions (Hi-Potion Tanks might save you gil)
• Level 10 NIN subjob
• 1 Boiled Crab or Fish Mithkabob
• 2 Hermit Wands
• a pair of Carbuncle Mitts (if these are difficult to obtain, add more Yagudo Drinks)
• At least 200 HP (250-300 HP would be ideal)
• Around 250 MP (add more Drinks if not)

Although you might not use everything above, you should still come prepared nonetheless.
 
General Information

• You will need a certain amount of fame to start this quest.
• You can repeat this quest after JP midnight.
• You can teleport to the battlefield directly by trading a Mini Tuning Fork to the non-Tarutaru NPC.

Battle Information

1. Avoid fighting avatars on their strong days. You might wish to avoid fighting on Darksday as well because Carbuncle is weakest on that day (however, I did not notice a huge difference).
2. If you win the fight, you will be given a scroll of Instant Warp to return home with.
3. You do not lose any exp upon death, so Home Point if you fall in battle. You do not want to be ejected into a high-level area with no way home.
4. Avatars have a very, very long agro range. Summon Carbuncle well in advance to avoid premature agro. 
5. Avatars can use "Blood Pacts" and cast tier II spells. They will usually unleash the former upon agro.
6. Avatars using "Astral Flow" deal approximately 184 damage per use on their non-strong days. With 220 HP, I had a decent chance at surviving these deadly abilities.
7. Avatars average 10 to 15 damage per melee attack, and each swing can inflict the avatar's respective "En-spell" effect for 20 to 30 damage.
8. Do not expect Carbuncle to deal more than 10 damage per hit. Given the enemy avatar has around 500-600 HP, most of your damage will likely come from spamming "Astral Flow."
9. Let Carbuncle chip away at your foe's HP until it is around 75%. Once Carbuncle begins the fight, you should retreat a safe distance and prepare to summon Carbuncle again. Rinse and repeat.
10. Once your enemy is around 75% HP, use a Yagudo Drink, and hit "Astral Flow" with a fresh Carbuncle. Make sure to stand close to Carbuncle during this time because enemy avatars tend to come for you immediately after. A non-resisted "Searing Light" deals around 210 damage, but at this point, you will need to chug Ethers to resummon Carbuncle.
11. Resummon Carbuncle, and stall your foe until you can use "Astral Flow" twice more.
12. If Carbuncle dies from your opponent's "Astral Flow" ability and you happen to be critically injured, chug Hi-Potions like no tomorrow. Try to resummon Carbuncle afterward, but be warned that it will take some time for Carbuncle to reestablish enmity.

Avatar-specific Information 














Special Moves: "Axe Kick," "Blizzard II," "Frost Armor," and "Diamond Dust" (Astral Flow ability).
 
Notes: Shiva and Ramuh both have access to high-tier Elemental Magic that can almost one-shot Carbuncle. In addition, Shiva can also use "Ice Spikes" to severely limit Carbuncle's damage output; however, other than that, she is similar to Garuda in difficulty.