The Archipelagore mutated creature does not have summoning sickness.
An opponent cannot block and kill the Archipelagore mutated creature.
Steps
At the beginning of combat, Captain Rex Nebula triggers, making the Archipelagore mutated creature a Vehicle and giving it Crew 2 and "Whenever this Vehicle deals damage, roll a six-sided die and sacrifice this Vehicle if the result is equal to its mana value" until end of turn.
Activate this Vehicle's Crew ability by tapping Captain Rex Nebula, making it a creature until end of turn.
Declare the Vehicle as an attacker and deal combat damage with it.
The Vehicle's ability from Captain Rex Nebula triggers, rolling a six-sided die with no chance of a result equal to the Vehicle's mana value of 7.
The Vehicle's ability from Brazen Dwarf triggers, dealing 1 damage to each opponent.