Question about a creature with Flash

[MrRW91]

Here is the scenario:

I have out a Dawnstrike Paladin (2/4 creature with Vigilance and Lifelink) enchanted with Trollhide (+2/+2 and Regenerate.)

On my turn, I play Hunt The Weak (Sorcery - "Put a +1/+1 counter on target creature you control. Then that creature fights target creature you don't control,) and assign it to attack my friends' Tower Geist (2/2 creature with Flying)

He uses Ambush Viper (2/1 creature with Flash and Deathtouch) as an instant to block my Dawnstrike Paladin.

My question is this: Since my Dawnstrike Paladin now has the ability to specifically choose a creature to block it, does Ambush Viper over-ride that? Or does Ambush Viper come out as an instant creature, but the Tower Geist still has to block due to my creatures added sorcery ability.

[Quisequise]

No attacking or blocking happens with the fight ability. The two selected creatures simply do damage to each other equal to their respective power.

[MrRW91]

So, the creature with less power (Tower Geist) is destroyed? Or, does the Ambush Viper block this play from happening, destroying my creature and the viper, leaving his Tower Geist untouched?

[particle]

flashing in the creature will not have an effect. you cannot block is response to "fighting" in {hunt the weak}. it is not like normal combat, where you can block.

[MrRW91]

My friend and I just started getting serious about practicing and getting better, so we are still unsure about a couple things. So you guys just helped answer two things for me, thank you.

[particle]

My friend and I just started getting serious about practicing and getting better, so we are still unsure about a couple things. So you guys just helped answer two things for me, thank you.

no problem. happy to help.