The Death Summoner and the dynamic trio.
Zintar Mortalis
If you are a person that's just starting out in Splinterlands, who wants to get a feel for the game before you want to spend any money or doesn't have the any DEC to rent from the market place. The best and easiest Summoner to use is ZINTAR MORTALIS. The summoner reduces attack by 1 to all melee monsters. That will keep your range monsters safe for a couple of turns. On top of that most death monsters have very low mana cost and high speed. In a lot of cases you will out number your opponent.
There's great synergy between Twisted Jester, Undead Priest and Death Elemental. They essentially deal 4 damages to mage or range minion in one turn and in most cases they will be dead. The most important thing is the placement of these monster. In general you want to put Twisted Jester in the back since he has high health and the Under Priest in the second spot as a meat shield. In a lot of low mana matches this lineup you will be in decent shape, but it still depend on what cards your opponent have. As you win a few matches and earn around 50 DECs, you can look to the market place to pick up a few low cost mutual card to help all your decks.
The Trio in action
https://splinterlands.com?p=battle&id=sl_70fd505a76fab142f1e260abb05f033c&ref=akstealth00