1. No, the arcane potions can't be used instead of the coloured affinity potions. You need them in addition to ascend. That's the case allready at the first ascension star.

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I would never buy this potions in the shop. The arcane keep, where you get these white potions, has opened every day, in addition to one of the affinity keeps.

2. Don't slow your progress down to much to do these missions. They don't run away. Just go on playing. You will have no problem later on to ascend a champion to rank 3.

The boss of the Magic Keep protects himself with a strong shield. The best way to deal with him his a champ that can remove or steal buffs. 

you know that you have a mixing potion option where you change 10 small for 1 medium, 10 medium for 1 big?

[quote=Skadi]

The boss of the Magic Keep protects himself with a strong shield. The best way to deal with him his a champ that can remove or steal buffs.  

[/quote]

Many, many thanks for the reply - you just saved me from wasting my gems on a misunderstanding!

Also, great tip - I hadn't realized shield's could be removed like that. I might try Mystic Hand in the Magic Keep to see if that helps speed up progress. :)

[quote=AzuraWrath]

you know that you have a mixing potion option where you change 10 small for 1 medium, 10 medium for 1 big? 

[/quote]

No, I haven't seen this feature anywhere. I'm level 30, so perhaps I haven't unlocked it?

if you look at skadi's photo in the above post, you'll see an icon with a potion on it labelled "Trankmischer" in the lower right corner. if you go into your tavern and click that icon, you'll open the potion mixer which allows you to merge smaller potions into larger ones.

Ah, excellent, thank you very much. :)

EDIT: Today I pulled Elhain from a Mystery shard and was able to ascend her to Level 3 to complete the mission by mixing potions. :)