Mulligans
General Mulligans
After starting the game and dealing cheap dmg with strong early drops you mostly have to give up the board and switch to a burn plan using the draw lava bursts and buffs.
Aggro Mulligans
zap with thunderhead or frog on the coin helps you stabilize if another aggressive deck takes control of the board earlier likkim is also 2 mana 9 dmg for 3 turns which kills almost every 1 and 2 drops by itself.
Control Mulligans
For control matchups it very powerful to lead with surging tempest into earthen might as most deck cant deal 5 dmg on turn 2-3. Vessina is fine against very slow decks for example Mage, but it's better to draw it naturally and fish for the early game as this deck wants to overwhelm the opponent early.
This is a more burn-based version of the aggro-shaman. The main keeps in the mulligan are frog as it lets you set up future burn lethal with doomhammer rockbiter weapon combo and lava bursts. Electra can be replaced by another unbound elemental but is a fine addition for finding lethal with lava burst.