Imo one of the best bosses of From's Souls library
And they accomplished it, with something they've seem to mostly have forgotten - simplicity
His moveset isn't extensive and is even quite basic
But it covers all bases - he has short, medium and long range attacks, AoE, charge moves and projectiles
Then, just when the player thinks he's got the hang of him... boom a double
Some might say a copycat enemy is lazy, which admittedly is correct to an extent - but even in the context of 2 identical enemies, the devs still need to make sure the clone meshes well with the original
Which it does, as again his moveset is simple but varied, so they can close each others gaps and more importantly don't end up being overcomplicated for the player - also due because by the time the 2nd one appears, the player has had enough time to learn the particularities of the moveset
Additionally, the splitting itself is long enough to serve as short pause between in the action (another important element From has mostly left behind in favor of constant spazz shit), which the player can use to heal and buff himself, or punish the boss
The AI of the two also mix things ups well enough - some times one is in the back casting projectiles, while the other keeps the players attention at short range ; other times they're both up an close, keeping pressure ; and sometimes both use their charge attacks
It helps immensely that every move is well telegraphed and there's no animation gacha trickery bullshit, even the few new moves they might do in this 2nd phase are all pretty much variations on the base moveset
Overall, just a fun and straigthfoward boss fight, with clever use of assets and solid design
