I've tried to make a less fragile Gnats list. Typically with Gnats you get smashed by Red but with this one you can win.
It has more healing with Guidance and Spirit Theft added. A Tiki Totem gives the Gnats another hit point the first time it respawns that turn (your turn and opponents).
The Lion Fish is the hard removal and is difficult to clear. It has Totem / Aviary / Guidance for buffs. Opponents will be reluctant to charge you down and smash the structures with this nearby.
The Carassius can get out of control and provide another sac target if you don't want to sac a Gnat.
You play a slow control style and eventually the Gnats will clear the board, or your life total.