User blog comment:Xeamnz/Dragon Rush deck?/@comment-24203014-20140121105240/@comment-11454852-20140121142015

IMO deckbulding and size ratios are more flexible than in Vanguard, since there's no riding mechanics that force you to find a specific card ratio at a specific turn, so you fee free to experiment a bit with ratios. However, some ratios can noticable change between different worlds, Magic is much more likely to run more spells and Danger is more likely to run more items, ect.

As for size 3s, as Hunter says no more than 6 should be fine.