Replicate

[Parasite]

i play Pyromatics (http://gatherer.wizards.com/gathererlookup.asp?set=Guildpact&name=pyromatics) and replicate it 3 times, then i play Twincast (http://gatherer.wizards.com/gathererlookup.asp?set=SaviorsofKamigawa&name=twincast)

does my opponent get 8 damage?

[Æther Reaper]

Replicate puts a new copy onto the stack. Twincasting the original pyromantics will only result in another copy. Your opponent will take 5.

[Aneximines]

Right. Replicate only triggers when the spell it's on is played, but Twicast doesn't let you play the copy it creates - it just creates the copy already on the stack, so the copy's replicate ability never triggers (incidently, this is also why the copies made by the replicate ability don't replicate themselves).

[Parasite]

so if i do understand:
i have weedragonauts (http://gatherer.wizards.com/gathererlookup.asp?set=Guildpact&name=wee_dragonauts) in play and i replicate Leap of Flame (http://gatherer.wizards.com/gathererlookup.asp?set=Guildpact&name=leap_of_flame) 2 times it gets +9/0 ?

[Aneximines]

so if i do understand:
i have weedragonauts (http://gatherer.wizards.com/gathererlookup.asp?set=Guildpact&name=wee_dragonauts) in play and i replicate Leap of Flame (http://gatherer.wizards.com/gathererlookup.asp?set=Guildpact&name=leap_of_flame) 2 times it gets +9/0 ?

No.

The 'nauts only get more powerful when you play an instant/sorcery spell.

The replicate copies aren't played. If they were, you'd have to pay their mana costs (or there would have to be a phrase like "without paying its mana cost" or something) in addition to the replicate costs you paid when you played the origonal spell. They just show up on the stack (similarly, if you put a creature into play with [card:80fef2fa25]Elvish Piper[/card:80fef2fa25]'s ability, you did not play that creature, so, for example, it wouldn't trigger [card:80fef2fa25]Glimpse of Nature[/card:80fef2fa25]).

[Parasite]

ok, thx a lot