It started as a guideline for my arena units only. Then, I got carried away.
14 BC[6]Brave Hero Alma [2667~2979]
15 BC[7]Crusher God Uda [4814~5376]
16 BC[7]War Queen Ophelia [4896~5468]
[8]Red Swordsman Farlon [4451~4971]
[8]God Eater Lira [4745~5299] (4564~5098 at bb9)
18 BC[7]Gaia King Lugina [4035~4507]
20 BC[1]Smith Lord Galant [2993~3343] (45% Weak)
[5]Omega Behemoth [4596~5133]
[5]Royal Guard Paris [4898~5470]
[6]Duelmex [11016~12303 random. lol.] (LS: 1.5x BC fill rate)
[6]Thunder Punt Zeln [3250~3630]
[6]Ice Warrior Karl [4934~5510]
23 BC[6]Felneus [4354~4863] (LS: 1.5x BC fill rate)
[6]Ultra Blade Aem [5261~5877] (LS: 3 BC per turn)
[7]Ray Sibyl Sola [3302~3688] (light & dark)
[7]Night Sibyl Madia [3740~4177] (dark, water & earth)
24 BC[10]Xenon & Estia [4179~4667]
[12]War Rocket Cayena [4218~4711] (45% Para)
[13]Gun Goddess Serin [4159~4645] (50% Injury)
25 BC[4]Noble Fist Dilma [6862~7663] (100% defense ignore for 2 turns. LS: 2 BC per turn & +30% damage on spark)
[6]Drake Angel Aisha [5700~6366] (LS: 3 BC per turn)
[10]Tyrant Goddess Phee [5014~5600] (+22% HC drop rate. LS: Large reduction in BB gauge required for BB)
28 BC[10]Black Lotus Lunaris [6940~7752] (45% Weak)
30 BC[6]Blade God Seria [4423~4940]
[10]Grahdens [5028~5616] (light & dark)
34 BC[9]Bordebegia [6856~7657] (+60% Spark. LS: 1.5x BC fill rate)
[10]Holy Blades Sefia [6872~7675] (45% Para. LS: +50% attack to dark & 1.2x BC fill rate)
[12]Death Idol Kikuri [6392~7139] (45% Curse. LS: +50% attack to light & 1.2x BC fill rate)
ARES LEADERS[6]Felneus [4354~4863] [23 BC] (LS: 1.5x BC fill rate)
[7]Crusher God Uda [4814~5376] [15 BC](LS: 1.5x BC fill rate)
[9]Bordebegia [6856~7657] [34 BC](+60% Spark. LS: 1.5x BC fill rate)
FIXED BC LEADERS[7]Sky Mage Rashil [2260~2560 heal] [20 BC] (+32% Crit. LS: 2 BC per turn & +50% BC drop on spark)
[4]Noble Fist Dilma [6862~7663] [25 BC] (100% defense ignore for 2 turns. LS: 2 BC per turn & +30% damage on spark)
[6]Ultra Blade Aem [5261~5877] [23 BC](LS: 3 BC per turn)
[6]Drake Angel Aisha [5700~6366] [25 BC] (LS: 3 BC per turn)
BB REDUCTION LEADERS[8]Ruin Goddess Zellha [9573~10691 stbb] [15 BC] (80% Weak. LS: Large reduction in BB gauge required for BB)
[10]Tyrant Goddess Phee [5014~5600] [25BC] (+22% HC drop rate. LS: Large reduction in BB gauge required for BB)
BUFFERS (1st slot units)[9]Empyreal Drake Lodin
BB: 20 BC cost(+8 BC & Thunder)
SBB: 20 BC cost [8996~10048] (+5 BC & Thunder for 3 turns)
[15]Goddess Axe Michele
BB: 18 BC cost (+110% attack & Fire for 3 turns)
SBB: 15 BC cost [10236~11432] (+115% attack & Fire for 3 turns)
[15]Duel-SGX
BB: 20 BC cost (+60% crit & Dark for 3 turns)
SBB: 10 BC cost [6764~7554] (+60% crit & Dark for 3 turns)
Source For arena, divide the BC requirement by half, and then rounded up. (23 / 2 = ~13)
Damage displayed are at bb10/sbb10 unless specified.