F.F. was obtainable for a limited time as a collaboration character in the mobile game Monster Strike.
F.F.
F・F
F・F
Sling Type: Pierce
Element: 
Rarity: 4★
No. 6411 
HP
10,944 (+1,400)
ATK
11,711 (+550)
SPD
281.20 (+13.60)
Ability
N/A
Strike Shot: "You can call me F.F.!"
Increases Speed. (12 Turns)
Bump Combo
Cross Stinger (Power: 7321)
Sentient Plankton, F.F.
知性を持つプランクトン F・F
知性を持つプランクトン F・F
Sling Type: Pierce
Element:
Rarity: 5★ (Evolution)
No. 6412 
HP
16,597 (+1,400)
ATK
13,729 (+1,350)
SPD
218.30 (+31.45)
Race
Demi-Human
Obtain
Evolution
Ability
Null Gravity Barrier / Super Null Warp / Demi-Human Slayer M
Strike Shot: "Foo Fighters"
Fires Foo Fighters at the aiming direction + Lowers enemies ATK and DEF for some turns. (16 Turns)
Bump Combo
High Cross Stinger (Power: 10250)
Female Prisoner Trio, Jolyne, Ermes & F.F.
女囚3人組 徐倫＆エルメェス＆F・F
女囚3人組 徐倫＆エルメェス＆F・F
Sling Type: Bounce
Element:
Rarity: 6★
No. 6432 
HP
18,174 (+3,900)
ATK
16,399 (+5,625)
SPD
327.50 (+102.85)
Ability
Null Damage Wall / Laser Stop / Null Warp / Multi-Hit Slayer
Strike Shot: "This game of catch isn't over yet!"
Splits into three clones + Attack the first contacted enemy with Stone Free and a ball. (20 Turns)
Bump Combo
Homing Pierce-struction 12 (Power: 3345)
The Stand form of Foo Fighters also appears as a non-playable boss character.
Foo Fighters
フー・ファイターズ
フー・ファイターズ
Sling Type: N/A
Element:
Rarity: N/A
Boss only
HP
N/A
ATK
N/A
SPD
N/A
Race
N/A
Obtain
Non-Obtainable
Ability
N/A
Strike Shot: N/A
N/A
Bump Combo
N/A