In Pokémon Platinum, the moves that Hoothoot can learn via level up include ones such as Foresight, Confusion, Growl, Tackle, Peck, Hypnosis, Take Down, Reflect, Zen Headbutt, Air Slash, Roost, Extrasensory, Psycho Shift and Dream Eater.
http://www.serebii.net/pokedex/163.shtml
no.
The same as in diamond &pearl
Yes he can. For example, he can learn the TM Ice Beam.
You can trade them to the move tutors so that your Pokemon can learn different moves.
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HOOTHOOT learns Peck, uproar, hypnosis and reflect and then at level 20 he /she evolves into Noctowl
if it was Pokemon platinum dialege leans arua sphere at level 92
all i know is mach punch and flame wheel and taunt
shards can be used to trade with other people. in return, they may teach your Pokemon moves. there are 3 move tutors in Pokemon platinum that will teach your Pokemon moves in exchange for shards in a specific color.
Arceus does not require an item in order to actually learn Grass-type moves, however it can be given the Meadow Plate in order to boost the power of these moves by turning it into a Grass-type Pokemon.
The best team in pokemon platinum is an Infernape, Staraptor, Luxray [third evolution of Shinx], Floatzel, Bibarel [make it learn all four moves as HMs] and Giratina.