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Assumption on merges and star level
As we get hero grail I think it is sure th assume no major changes for merges or 5* remaining the maximum. I don't think IS will give us new units we start building up for 5+10 just to have them all reset to 0 merges by releasing 6*in a month.
Therefore I would suggest it is safe to merge now.
Thinks that could happen though might be either an increased max merge or some kind of ascending. That would fit the development and life cycle of many other haha games by the way ;)

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