seems like eveyone forgot combining two-headed with twin universe, for a 4x damage, rather than 3x (with 2 tu's)
phoenix + adrenaline + momentum + two-headed + pu + pu = unupped otk with 6 cards and 1 high-cost element.
if what keolino said about turns, rather than attacks, we can get it even more interesting:
ruby dragon + unstoppable + sky blitz + two-headed + tu + tu = 6-card fg otk.
silurian dragon + two-headed + mitosis + SoR + tu + SoR + sky blitz + chimera = 312 damage.
also, what happens when using 2 two-headed's on 1 creature? will it cause both attacks to deal damage twice?
Spoiler for if double two-headed causes 4 times damage:
elite charger + two-headed + two-headed + two-headed + two-headed + two-headed + two-headed + tu = 7*2^7=896 damage.
for 5
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, 24
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, and 6
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.
in order to get a fg otk this way, you need 5
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and 20
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, with 6 cards.
In terms of damage/card, you could go with ruby dragon + unstoppabe, for up to 1024 damage;
using sky blitz and tu, you can get the costs down to 12
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, 1
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, 16
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, 6
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and 8
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. edit: in case you want to use SN.
I somehow think that this will not be the case...
You can do the same trick with pu as you said, but with 3x instead of 4x, is not a big deal
And a two-headed creature if targetd again won't receive any bonus
P.S. Increased cost to 6|5