As mentioned under Complacent Gaming Syndrome, Ōtengu and Ubume (with Seductress soul and tons of crit) are used by everyone, even better if at the same time, because they're simply overpowered.
A Higanbana built for CC is just annoying to fight. She lays down a carpet of damaging flowers at the start of the battle, she will always hit the enemy before they get a chance to act. If built with enough Effect Hit and a disruptive soul like Temptress or Shy Soul she can literally cripple the enemy team without even letting them take a single action. Because the CC is always refreshed every time the enemy takes an action, it can't be cleansed out of either. It even bypasses Ootengu's Wings of Steel passive, which is supposed to allow him to ignore the first CC he takes every turn, because his Shelter protection expires at the start of his turn (before the damage hits) before reactivating again at the end. There are very few, very specific counters to CC Higanbana and none of them are 100% reliable, especially if the Higanbana has been leveled up enoughnote Effect Resist boosts like Kamaitachi and Aobozu can still be overwhelmed if she has enough Effect Hit and Sea Spirit's passive shield will still fail if Higanbana is powerful enough for her damage to exceed 10% of the target's max HP. The only guaranteed protection is to Morph or Seal her, disabling her passive, but even that can fail if she has enough Effect RES herself.
Speaking of horrific SSR power creep, Onigiri seems to have been a result of the developers looking at Tamamo and saying "Yeah, we can do better than that". Simply put, his passive effect is just flat-out unfair. While he simply does absolutely horrendous amounts of damage with just his basic attack, his passive takes this to new heights with free strikes that deal terrifying Splash Damage that bypasses most manners of shielding, or Shōzu's Life-link. When built right and allowed to attack, his first move is a practically-guaranteed win, especially when equipped with Scarlet soul (counter attack on damage), so you'd better be damn sure your shikigami could off him in one move, or it's game over. Disabling him with controlling effects is the only remotely-viable way of shutting him down, which is harder than it sounds since his Evolution bonus is an increase to Effect RES, on top of the defensive buffs granted by his team. As a result, he really should be at the top of this list, as shortly after his release he became effectively the only DPS shikigami anyone bothers using at high levels (some players even use multiple copies, on the basis that if one OP shiki is good, 2 OP shikis is better). It got so bad that (rather than nerfing him, oddly) the developers had to release Hakuzōsunote A defensive shiki optimised to negate single-target damage, which prevents Onigiri's follow-up strikes as a hard counter to him. And even then, he's still dominant.
Momo-no-sei and her Healing HandsandBack from the Dead skills, 'nuff said (and for that matter, A.I. Sakura with her skills). If you see her in your enemy team, it's especially painful if that team also contains a powerful attacker. Kill the attacker first and she will bring them back; kill her first and the attacker will have more chance to act. To make matters worse, her healing scales off her HP so (aside from the Crit soul she will have in her slot 6 to facilitate her teamwide heal) she will always be built with massive amounts of HP, making her probably the toughest shiki on her team. The only solace? Her Back from the Dead skill has a cool-down.
Kurodōji, whose special skill is stronger the lower his HP is; God bless you if he gets a chance to strike at your team when he's a millimeter away from dying. Worse yet, his passive means that he can Counter Attack you with his special skill without even using mitama or spending mana at all. Even worse yet, if anyone is killed by his special skill, he'll slash at your team again until no one else dies. HEHEHEHE indeed.
His friend Shirodōji isn't far behind. His multi-target blast is followed by generating a shield for all members on his team that allow them immunity from the first attack they get, making single attacks on them useless regardless of how powerful they are. Worse yet, if powerful attackers on either side fall before he does, his blast can bring them all back for one turn to hit the opposite team. Even worse yet, once Awakened, every time an opponent falls, he'll automatically hit another opponent with his basic missile attack.
Less frequently used than most, but Shoyō is pretty damn terrifying. What makes him powerful is his "curse", which collects damage dealt to the victim and activates upon his second turn after casting, dealing a share of the memorized damage to the opponent. You're under his curse and the strong attacker on the opposing side failed to kill you, only leaving you within an inch of your life? Don't get too excited, because You Are Already Dead; come Shoyō's turn and you'll be finished off anyway. That is still not the full extent of this skill's power; it bypasses Shōzu's Synchronization, meaning that the collected damage will not be split among the team and will be fully dealt to the victim. The worst part? It cannot be removed via status-effect-removal skills and it bypasses status effect immunity. Not even enemies like Orochi (no, not the humanoid SSR) or Octopus are safenote As a result, his most common use is to deal with powerful world bosses. To top it off, both his special skills, one of which casts the curse when sufficiently upgraded, only cost 2 mana points each. He is especially powerful when fighting any Demon King style battles where you'd want to score as much damage as possible.
Players who like to spam Herd-Hitting Attacks would soon learn to fear the name and sight of Hitotsume, whose Diamond Sutra has the potential to reflect up to 120% of their attack power right back at them and causing them to melt from their own damage. And he's an extremely common R-grade shikigami to boot.
After a skill rework, Chin became one of the most OP shikis in the entire game, enough that she absolutely dominates any boss challenge. Chin on her own isn't that big of a deal- when she attacks a target, she gives it 2 stacks of her poison which do HP% damage on the target's turn. However, when her passive reaches the maximum level, any attempt to apply poison stacks to a target that already has the maximum of 5 instead does a massive burst of damage equal to 30% of the target's maximum HP (capped at 280% of Chin's ATK). Now, consider that poison stacks from multiple copies of Chin all count as the same effect and you're beginning to see where this is going. Equip your 2-3 copies of Chin with the Scarlet soul (counterattack on receiving damage, including transferred damage, itself universally considered completely broken), throw in the aforementioned Shouzu to ensure that any hit on any of your shikis will trigger a counterattack from your Chins, and watch enemies just get torn to shreds. While somewhat limited in PvP, when fighting targets with massive amounts of HP like area bosses the Chin-stacking strategy is often literally the only one worth using, as any glance at the damage leaderboards will universally show.