There are some looping combinations that you can build with fairly common troops:
Hellcat/Alchemist + any combination of red and yellow troops. 2x goblin rocket is good (you do damage, move the board around and keep the turn), Gard’s Avatar or The Worldbreaker are great if you have those mythics (big damage to all 4 troops). Queen Titania does damage to all 4 and can keep the turn if there are 13 or more red gems on the board.
Green Seer/Giant Spider + any combination of green/purple troops. 2x Kraken is great (with the 3rd trait, you do 6 damage to all troops on every loop), Boar Rider, Goblin, Princess Fizzbang or any other Goblin that uses green or purple (you do damage without giving up the turn and go back to looping).
The idea with both of these is to keep casting the first two troops back and forth to repeatedly fill them while giving yourself extra turns from 4/5 matches with the transformed mana gems. The extra mana that you generate fills the 3rd and 4th troops which you can use to do damage with extra-turn troops or do heavy damage with things like Gard, TWB, Kraken, etc. at the risk of giving the opponent another turn.
It can take a bit of practice with these looping teams to learn to really control the board, but it is a very effective strategy as long as there is no Queen Mab on the other side.