Someone suggested preventing you from getting Flail Whip before Chain whip, and possibly Angel Shield before Silver Shield.
This might solve the problem of some people getting early Flail in a seed and having it remove all the challenge, so it's likely to be implemented at some point.
Dev note: This should be entirely doable by adding a second copy of the chest/item/conversation/shop and adding a flag check to both instances (one for having collected chain whip, one for not). In the case of shops, may need another instance so that the one you purchased is the one that continues to appear. Could also have some inconvenient interactions with Sacred Orb shops.
Someone suggested preventing you from getting Flail Whip before Chain whip, and possibly Angel Shield before Silver Shield.
This might solve the problem of some people getting early Flail in a seed and having it remove all the challenge, so it's likely to be implemented at some point.
Dev note: This should be entirely doable by adding a second copy of the chest/item/conversation/shop and adding a flag check to both instances (one for having collected chain whip, one for not). In the case of shops, may need another instance so that the one you purchased is the one that continues to appear. Could also have some inconvenient interactions with Sacred Orb shops.