Konstantinos XI

If Master wants to get their Michael to functional levels, 6/6/6 is a good enough stopping point, as Constantine doesn’t warrant enough return for bigger investment compared to other Servants. 6/6/10 would be good subsequent point as his third skill is by far his strongest skill, while 6/10/6 is also an acceptable alternative to focus on his supportive aspect more. 

• Hagia Sophia's Prayer C- - This is his main utility skill, the real value of it comes from the Target Focus when used in conjunction with his Noble Phantasm, but beyond reducing the cooldown for better uptime, the value in leveling it is rather miniscule.
• Empire's Decline EX – Constantine’s main teamwide buff skill and it is rather potent due to it being 3 turns and him benefitting from all three effects. This is a good skill to prioritize especially if the Master uses him with other [Roman] Servants like Romulus-Quirinus.  
• Demise Privilege C – Having NP Charge on it already makes this skill a higher priority compared to his other skills, especially considering Constantine is a Buster-centric Servant with not particularly outstanding NP Generation. The On-Death buff effect can be combined with some rather niche synergy such as with Chen Gong or Taunt Craft Essence.

“You are my Master. Although I was an emperor in the past, it has no bearing on our current standings.”

The Marble Emperor of the Western Roman Empire, Konstantinos / Constantine XI (or for a more endearing name, Michael) was a fascinating figure that embodied the last spurt of blazing glory of a great empire. Famed for his last struggle against the Ottoman army, Constantine XI’s kit represents this via a combination of teamwide defensive effects and Buster Critical Support.

If there was a good word to describe both Constantine XI’s reign as well as his skill set, it would be transient. Most of his buffs, while somewhat strong, are not long-lasting. Hagia Sophia's Prayer C- increases his NP Generation Rate for 1 turn, grants Target Focus to himself for 1 turn and also provides a sizable amount of Critical Stars immediately. Empire's Decline EX improves all allied Servants’ Attack and Buster cards’ effectiveness for 3 turns, and further improves all allies with [Roman] trait’s Critical Damage for 3 turns. Demise Privilege C is Michael’s most unique skill, as it grants him NP Charge, a 3 turns Critical Damage Boost, a 3 turns Critical Stars Regeneration and for 3 turns, and if he is defeated he will buff the ally in the rightmost position with the exact same buffs. Theodosius Kōnstantînos B+ is Constantine’s Noble Phantasm, reenacting the protection of the famous Wall of Constantinople as a blessing to both himself and the team. This non-damaging Buster Noble Phantasm grants a Buster card effectiveness buff for 3 turns and 1 turn of Invincibility to Constantine XI, while also increasing his allies’ Defense massively for 1 turn, and any [Roman] ally receives an additional 1 turn Damage Cut buff. This Noble Phantasm makes him an effective Single Target tank for a turn for his teammate when used in conjunction with his first skill Target Focus effect.

While Constantine XI provides a lot of buffs, he suffers an identity crisis in what his kit is supposed to do. He is quite bulky, has decent offensive self-buff and defensive team wide buffs, and can lean into doing strong Buster Critical Hits. However, Michael does not excel in any role and struggles to stand out in any of these niches. He doesn’t hit as hard as a dedicated Buster Critical Damage Dealer in the mold of someone like Quetzalcoatl, does not provide enough defensive support on a regular interval like Merlin or bring strong offensive and utility tools to the whole party like Taigong Wang. Thus, it’s hard to find a real place for him in any developed roster as more and more specialists are released.

Overall, the lack of specialization in modern FGO is a major flaw for any Servant to avoid the pitfall of being forgotten in terms of gameplay. While Constantine is certainly far from being a bad Servant, his lack of a real potent role that he could excel in makes him a relatively awkward Servant to utilize. Nonetheless, in terms of spectacular drip and cool factor, Michael has those in spades.

Good Team Wide Buffs

Constantine XI provides a plethora of teamwide buffs from his skills and Noble Phantasm, including Attack, Buster card effectiveness, Defense and further improving [Roman] allies with Damage Cut and Critical Damage buffs. Furthermore, he also generates a lot of Critical Stars by himself with his first and third skill, and can act as a pseudo tank for the team with his Noble Phantasm + 1st skill combo. With his third skill, when he retreats, he can provide a strong single target buff to a Servant of choice as well.

Exceptionally Bulky

Thanks to his high base HP and a lot of defensive buffs in his kit ranging from Invincibility, Damage Cut and Defense Up, Constantine IX is very durable and geared toward difficult content. This alleviates a lot of pressure in high pressure situations compared to more conventional Damage Dealers.

Decent Critical Buster Niche

Constantine IX does have tools to be a decent Critical Damage Dealer. His natural starweight is high, he has good Critical Star regen via his skills, and several offensive self-buffs. These buffs can also also partially extend to his allies as well, especially any strong [Roman] Servants with the same niche such as Romulus-Quirinus.

Lacks A Real Niche 

Constantine XI tries to do all too many things at once but does not distinguish himself in any of those. In Challenge Quest settings, there are better damage dealers and defensive supports available, and in some cases, characters that excel at both better than Constantine IX, making it hard to justify a place for him when team slots are so competitive and rosters are getting bigger and bigger.

Short Duration on Buffs

Several of Constantine’s buffs and effects are only one-turn, namely those from his first skills and Noble Phantasm. Since he is not exactly a looper, and the effects aren’t strong enough to justify such a poor buff uptime, it makes Constantine IX’s effect on the battlefield a lot more limited.

There are two main ways to play Constantine. Master can either play him as a bulky Buster Centric Attacker - Tank hybrid for Challenge Quest or as a suicidal buffer for a specific ally via his 3rd skill effect. For the first playstyle, Starting NP Gauge, Buster Card Effectiveness, and Critical Damage are great stats to look for. For the second playstyle, either Target Focus effect to quickly trigger his third skill or any Craft Essence with an effect that can Trigger On Death would be a good alternative. Critical Star Regeneration effect is also a good choice to make him a good passive Critical Star Regeneration in conjunction with his 1st and 3rd skills to support another Buster Critical Damage Dealer

• Victor of the Moon / Joint Recital / Box of Repentance / Dancing On Lotus Blossom / Maiden Leading Chaldea / No Strings: These Craft Essences focus on Buster Crit niche and are fitting choices if the Master wants to accentuate his damage output.
• The Merciless One / Battle of Camlann: These Craft Essences have the best Trigger on Death effects that Constantine can tap into for creative clears.
• GUDAGUDA Poster Girl / Grand New Year / Halloween Arrangement / Outrage: Craft Essences with an additional Target Focus effect to help Constantine serve as a tank for his teammates and trigger his third skill effects easier.