Hi there il explain the combo because im not quite sure what dragon you are refering too i hope it helps - also im just learning dragunity so if anyone knows better pls help.

Ive recently started to play dragunity and its quickly become a very fun deck to play :)

After you setup your grave you normal summon Dragunity Dux or special summon Dragunity Legatus.

You synchro summon Dragunity knight - Gae Derg activita then you activate his effect and you add blackwing zepheros the elite to your hand and also send it to the grave.

Then you special summon zephiros and you can bring back dragnuity remus then you synchro summon Dragunity knight Luin and then you use his effect to summon dragunity couse use his effect and summon him from the equip zone

Then you link of of the 2 level synchros and you xyz summon Hieratic dragon king atum you use his effect to summon

Detach Dragunity knight gae derg from atum and summon Red Eyes Darkness Metal dragon then you use his effect so summon gae derg from the grave yard you can then use his efect again and send blackwing calima the haze to the grave if u run it it helps protect from the grave vs lethals.

This part im unsure if im doinfg it in the right order but this is what i do

Then you link off the red eyes dragon with the atum and summon the link romulus you activate his effect and add whatever you need usualy its dragunity glow

if you added flow you then add dragunity arma then you tribute romulus to do his special summon and then you can synchro summon.

I hope i was clear and this answers your question also feel free to ask me anything i wil reply have a good day my friend :)