No merge statement. You'll have to write seperate update and insert statements. Something like this

Update table2 set f1 = table1.f2*0.1

FROM table1 where table2.f1=table1.f1 and table1.f1=20

INSERT Into table2 (f1, f2)

SELECT f1, f2*0.05 FROM table1 where not exists (select 1 from table1 where table2.f1=table1.f1 and table2.f2=table1.f1 and f1=20)

those should be equivalent, but they are untested and I'm not completely familiar with how oracle's merge works