1.dragoncaller will not let other atk boost apply while it should, in example if its fused with buster blader, dragon destroyer swordsman.
fusion summon buster blader dragon destroyer swordsman with dragoncaller magician and attack a dragon opponent controls. its atk will be 5600 while it should gain 1000 for eaxh dragon by its own effect
Q: Player 1 Fusion Summons “Buster Blader, the Dragon Destroyer Swordsman” using “Dragoncaller Magician” as Fusion material. Player 2 controls a face-up “Baby Dragon” in Attack Position. Player 1 attacks “Baby Dragon” with “Buster Blader, the Dragon Destroyer Swordsman”. What should the ATK of Buster Blader be during the Damage Step?
A: Buster Blader initially gains 1000 ATK due to 1 Dragon-Type monster on the field. However, during the Damage Step, its ATK becomes double its original ATK, so 5600. Buster Blader changes Baby Dragon to Defense Position. The piercing damage received by Player 2 is 5600 ATK - 700 DEF = 4900.
This confirms that the 1000 ATK increase for each Dragon-Type monster does not re-apply at the Damage Step.
This is indeed in conflict with the pre-MR4 database ruling here with Megamorph vs Flash Assailant where Flash Assailant’s continuous effect did re-apply at the Damage Step: https://db.ygorganization.com/qa#6248 (2017-03-24)
I have to go by the latest rulings received. The megamorph ruling was 3 years ago.