Heart guy: Answer as you are
You answer the door as you are, acting as though everything were perfectly normal.
"We have your-"
"What are you supposed to be? A demon? Where is this man's woman?"
Pay more attention to Heat Guy
We take a look at what Heatguy's up to, but not too closely. Because Heatguy is not a stick figure with a hat and therefore we will ignore him. He is very unimportant indeed and we will surely not be returning to see what he's doing ever again.
Make a propeller out of the black hole guy and fly towards the ocean
You have no idea where you would find an ocean around here. Still, fly you shall.
You grab some bits of wreckage from the ruined tank and bend them into makeshift propellor arms.
summon another tank.
You're too far away from land to deploy the tank there, so you just place it in midair and let it fall.
Tell us how Black Hole guy came to be
Black Hole guy never "came to be". Nor did any stick figure. Instead they are themselves from the future. Hang on, let me draw a diagram...
At some point in the future, every stick figure will inevitably go back in time and become their past self, either by dying and respawning in the past or through some time travel power. So there's no point at which they "come to be".
For some, that's the whole story (ignoring Limbo): Go to future, die, respawn in past, repeat. As you might expect, that's not where it ends for everyone.
See, stick figures respawn at a random time and place, so they can die any number of times before ending up back where they started. And every moment they're chasing the trail left by themselves in the future in an endless ouroboros of fate.
Of course, they can't remember the immediate future. As time passes after an event (from their perspective), they forget details of the event. After half their lifetime has passed, the event is totally forgotten. So if they live for a total of 80 years, they may or may not remember the past 40 years, but the 40 years before that (which is also the next 40 years) is guaranteed to be forgotten, and is marked in red on the diagram.