From my experience I found
- When you start merging pet with 1-20 merges should use merge spirit because it will increase savy and rank alot.
After that you must merge the normal pet 3-10 times before merge to main pet.
To merge normal pet no need merge spirit. I will merge my main pet when status/rank is increase at least 0.8 (including merge spirit).
That is the way to make you merge become more effective.
