You can flicker Terastodon in respond to the fight ability, put it will only mean you wasted the tactics as fight has a requirement that both creatures have to still be there for the damage to happen
CR
701.10. Fight
701.10a A spell or ability may instruct a creature to fight another creature or it may instruct two
creatures to fight each other. Each of those creatures deals damage equal to its power to the
other creature.
701.10b If a creature instructed to fight is no longer on the battlefield or is no longer a creature, no
damage is dealt. If a creature is an illegal target for a resolving spell or ability that instructs it to
fight, no damage is dealt.
701.10c If a creature fights itself, it deals damage equal to its power to itself twice.
701.10d The damage dealt when a creature fights isn’t combat damage.
CR
701.10. Fight
701.10a A spell or ability may instruct a creature to fight another creature or it may instruct two
creatures to fight each other. Each of those creatures deals damage equal to its power to the
other creature.
701.10b If a creature instructed to fight is no longer on the battlefield or is no longer a creature, no
damage is dealt. If a creature is an illegal target for a resolving spell or ability that instructs it to
fight, no damage is dealt.
701.10c If a creature fights itself, it deals damage equal to its power to itself twice.
701.10d The damage dealt when a creature fights isn’t combat damage.
I buy HP and Damaged cards!
Only EDH:
Sigarda, Host of Herons: Enchantress' Enchantments
Jenara, Asura of War: ETB Value Town
Purphoros, God of the Forge: Global Punishment
Xenagos, God of Revels: Ramp, Sneak, & Heavy Hitters
Ghave, Guru of Spores: Dies_to_Doom_Blade's stax list
Edric, Spymaster of Trest: Donald's list
-K