list of variants on 2.9 that i've used or seen pros use at some point:

• 2.9 i.e. xbow, tesla, ice golem, archers, ice spirit, skeletons, fireball, log
• knight over ice golem aka 3.0. I've used this one the most
• rocket over fireball
• knight over ice golem, musketeer over archers
• knight over ice golem, musketeer over archers, rocket over fireball
• knight over ice golem, musketeer over archers, goblins over skeletons
• knight over ice golem, musketeer over archers, rocket over fireball, skeleton army over skeletons, arrows over log, fire spirits over ice spirit. I use this in triple elixir war day collection
• knight over ice golem, inferno tower over tesla, fire spirits over ice spirit