On DMM only drake from event and campaign should more than enough to use.
Grind for drake is not necessary, I think.
Except you got tons of slice unit in game and you want to evol them all, grinding is need.
You'll have more than enough, so much that you won't have enough gold instead despite for whole gold x2 last week
FKG ID
DMM ID: 561075604 (106/107)
IGN: Dusk
[Just a guy with bad self control and blow his gems for more salt and sodium chloride]