Although zero mana cards can be used as filler cards in battles that have a lot of mana available, the best way to take advantage of the use of these cards is when we are in battles that have low mana consumption, since we can complement the empty spaces, in this way the cards that do not consume mana, will serve as a decoy and also as a filler card.
This way it is possible to avoid direct attacks to our main cards, which allows us to obtain certain advantages over the opponent.
Example of the use of zero mana cards.
Normally, I usually use earth and water element teams, that's why I use Fungus Fiend and Torrent Fiend, besides that I use a neutral card in order to get two zero mana cards, i.e. I mean Furious Chicken. In the following battle we can get an example of this kind of combinations with water element cards and facing a death element team. In the end the zero mana cards fulfilled the objective, as they filled the spaces and functioned as a decoy card.
How Rebellion cards improved the strategy and use of zero mana cards.
Since the cards of this edition started to be used, it is now possible to improve this type of strategies, since the summoners allow to summon cards of two different elements. This makes it possible to use up to three zero mana cards. In this way it is possible to complete or fill empty spaces, basically it is a way to place cards in a free way.

In the previous battle, I used the summoner Zeddica from the Rebellion edition, so I could combine three types of cards from the water element, death and neutral, at the beginning I placed three cards and the last three spaces left over I filled them with the zero mana cards (Torrent Fiend, Furious Chicken and Corpse Fiend). At first the decoy cards prevented my main cards from taking damage. There is no doubt that these types of cards are very useful.
Conclusion.
As I had already mentioned, previously it was possible to use two zero mana cards per team, now with the new Rebellion edition, it is possible to make use of up to three zero mana cards, which helps us to obtain a better performance in low mana battles. In addition to that, if we know how to use or combine the right skills, it is possible to strengthen the zero mana cards, either by using cards that increase or restore the shield.
The images were captured from the Splinterlands.
I hope I have fulfilled your expectations and that you have enjoyed watching my publication.
Written in Spanish and translated with www.DeepL.com/Translator (free version)