Chrono Trigger has been covered much more comprehensively by other people than I can. For better information you should probably seek out other guides; several excellent CT FAQs exist and will fill you in on the events and inconsistencies of the game more effectively than I can. This section is merely a desultory effort by myself to appear less biased toward Chrono Cross.
a. IS IT MY IMAGINATION, OR ARE THERE WAY TOO MANY PARADOXES AND IMPOSSIBLE/
INCONSISTENT TIME WINKLES IN THIS GAME?
It certainly seems that way - the biggest irritant being the inconsistency of how Crono's actions change the world. Here's a list of oddball paradoxes in the game. It's things like this which make time travel plots such a pain in the butt.
EVENT PROBLEM & POSSIBLE SOLUTION
Crono participates in a pivotal Defeating Azala allows humans to gain battle which determines the the upper hand in the battle of evolutionary fate of the planet evolution. But it's Crono's role in the and which hominid species ends battle which tips the scales in the up at the top of the food chain. favor of humanity. So how could Crono
have been a human to begin with? It's
a closed event loop - human Crono
would never have existed had the
Reptites never lost out, but the
Reptites never would have lost had
human Crono never been involved.
HOWEVER...
Azala mentions that the temperate
change caused by Lavos' impact would
have been deadly to the exothermic
Reptites in any case. So take that
extra ending in which Crono is a
Reptite in the spirit in which it was
intended - a joke. Crono helped win a
battle, but the ultimate fate of the
Reptites was sealed by Lavos.
The magic chests which hold secret Taking an item from a chest in A.D. items can be opened in later time 600 should make it impossible to periods, then opened again in the acquire that item in a later period. past. But if Crono already has opened a
chest in the future when he opens
it again in the past, the item he took
from the chest in the future doesn't
disappear.
HOWEVER...
Those chests are sealed by a magic
related to Schala's pendant, which was
designed by Balthasar as a time-
traveling device. Who knows what arcane
powers were imbued within the chests as
well, eh? In other words, it's not a
big deal.
Crono gives Frog the courage to stop Magus failed to summon Lavos in any Magus from summoning Lavos in A.D. case, as he is unaccounted for in the 600. untampered A.D. 1000 and the Mystics
rue his failure to call Lavos. When
Crono and Frog interrupt his summons,
Magus is pulled back into 12,000 B.C.
by Lavos. But had Crono never become
involved, Frog would never have
reclaimed the Masamune or the Hero's
Medal and Tata would have been the one
to face Magus. It seems somewhat
unlikely that Tata would have been able
to best Magus' generals and stop Magus,
yet somehow Magus was unable to call
Lavos even before Crono traveled to the
past. Even if this is not a paradox, it
is poorly explained.
The Black Omen appears only after When Queen Zeal raises the Ocean Palace Crono dies in 12,000 B.C., never to create the Black Omen, the airborne having been a part of history fortress appears in every subsequent prior to his interference in the era as well. But prior to Crono's trip past. Yet Crono and Magus exert to 12,000, no Black Omen existed in only minimal influence upon that later eras. The Queen's scheme was to era, failing in every way to stop use the Mammon Machine to tap into Queen Zeal's scheme to summon Lavos. Lavos' power, and it can be assumed
she was successful in summoning the
alien menace to some degree as certain
results of her actions - the Gurus
being scattered throughout time, for
instance - had already transpired
before Crono ever began his time-
traveling exploits. So why did the
Black Omen rise only after Crono was
killed fighting Lavos? Magus alone
would have been incapable of stopping
Zeal and Lavos if he was incapable of
stopping them with Crono's help. The
presence of the Black Omen after
Crono's death is confusing and
inconsistent.
HOWEVER...
The only explanation I can posit is
that the energy Schala expended to
protect Crono's team from Lavos would
otherwise have been directed toward
destroying the queen and her machine,
thus preventing the Black Omen from
rising into the sky.
Magus as the Prophet in 12,000 doot B.C. obviously draws upon his knowledge of the era from his childhood memories. Yet he predicts the arrival of Crono's party, even though he couldn't have known that Lavos' warp would lead them to the same era as him
The doozy: Marle's accidental doot incursion into 600 B.C. causes her to erase her own existence when she's mistaken for her own ancestor.
Incidentally, the best explanation for all of these paradoxes is "don't think about it too hard - it's just a game."