We photometrically observed three dwarf novae V877 Ara , KK Tel and PU CMa .
We discovered undisputed presence of superhumps in V877 Ara and KK Tel , with mean periods of 0.08411 ( 2 ) d and 0.08808 ( 3 ) d , respectively .
Both V877 Ara and KK Tel are confirmed to belong to long-period SU UMa-type dwarf novae .
In V877 Ara , we found a large decrease of the superhump period ( \dot { P } / P = - 14.5 \pm 2.1 \times 10 ^ { -5 } ) .
There is evidence that the period of KK Tel decreased at a similar or a more exceptional rate .
Coupled with the past studies of superhump period changes , these findings suggest that a previously neglected diversity of phenomena is present in long-period SU UMa-type dwarf novae .
The present discovery of a diversity in long-period SU UMa-type systems would become an additional step toward a full understanding the dwarf nova phenomenon .
PU CMa is shown to be an excellent candidate for an SU UMa-type dwarf nova .
We examined the outburst properties of these dwarf novae , and derived characteristic outburst recurrence times .
Combined with the recently published measurement of the orbital period of PU CMa , we propose that PU CMa is the first object filling the gap between the extreme WZ Sge-type and ER UMa-type stars .