An abyss.
there was a bottomless hole of dirt and bugs
Bottomless Trap Hole does not target, so Tyrant Dragon is unable to negate it.
Bottomless Trap Hole does not target due to the way it can remove multiple monsters. If Bottomless Trap Hole is activated, then Stardust Dragon can be used against it, even if Bottomless Trap Hole was activated in response to Stardust Dragon's own summon.
they are black and their bottomless!
Yes, it is a Quick Effect and can be chained to Bottomless Trap Hole.
Yes, it can. However Bottomless Trap Hole is a card that destroys, so Stardust Dragon can be used to negate it, even if it was used in response to Stardust Dragon's own summon. The Bottomless Trap Hole will be negated and destroyed in that case.
It depends on the circumstances. Generally, "Bottomless Trap Hole" will be the better card; it works on Special Summons and it removes the monster it destroys from play. However, "Trap Hole" has one advantage: the monster summoned only needs 1000 ATK to trigger it, whereas "Bottomless Trap Hole" requires at least 1500 ATK. So, it would depend upon the type of deck you planned to use or went up against, but most people would choose "Bottomless Trap Hole".
Bottomless Trap Hole destroys monsters as well as removing them, meaning Stardust Dragon can chain to and negate it.
anything without a bottom is not a hole, but a tunnel.
A Fusion Summon is considered a special summon, so anything that can respond to a special summon (such as Bottomless Trap Hole) can be used against it.
yes You can
Obsidian Dragon only negates S/T cards that 'target' one Dark monster on the field. Bottomless Trap Hole does not target, Obisidian Dragon cannot protect against it.