If you have a flying weapon and a crusader on your field, and you cast sky blitz and then endow the weapon. The weapon gains the double damage but the crusader only gains the standard (not doubled attack). This seems like it should be consistent behaviour, so I did some looking and found the following:
TU+Sky Blitz - TUing a sky blitz creature (or animated weapon) creates a permanently buffed creature. That is, after one attack, the original will return to normal attack and the new copy will remain (This may be a bug in itself). The attack is treated as doubled.
BE+Sky Blitz - Using Butterfly effect will allow targeting on a 2 attack creature (flown dagger or druidic staff). Using sky blitz will buff the attack to 4, at which point it cannot be targeted by BE. The attack is treated as doubled.
Antimatter+Sky Blitz - AMing a blitzed creature (or animated weapon) makes the weapon heal for double its damage for 1 turn, before healing for ts normal damage. That is, a flown blitzed AMed short sword would heal for 6 and then 3 each turn after. The attack is treated as doubled.
These are the only cards I could think to test, but each treats the double attack as a double attack whilst it is. Crusaders on the other hand, take the unbuffed stat, but only for Sky Blitz, other buffs count.
Further proof, I had 2 flown titans (upped), 2 crusaders, 2 rage elixirs and a sky blitz. I used a rage elixir on 1 titan, sky blitzed then used the other elixir on the other titan. Now I had a 28 (rage before blitz) attack titan and a 22 (blitz before rage) attack. I endowed both titans with a different crusader, and both crusaders got a 14 attack boost.
