You have a green creature card in hand with mana value equal to seven.
Marwyn does not have summoning sickness.
You have enough mana to cast the creature card in hand, minus ({1} magic symbol) .
Steps
Activate Marwyn by tapping it, adding an amount of ({G} magic symbol) equal to Marwyn's power.
Cast any creature card in your hand with mana value seven by paying its mana cost.
Raggadragga's second ability triggers, untapping Marwyn and giving it +7/+7 until end of turn.
Activate Temur Sabertooth by paying ({1} magic symbol) ({G} magic symbol) , returning the green creature with mana value seven from the battlefield to your hand.