YOU WIll NEED ROCK SMASH FOR THIS!
Go to the city north of the one you start at(sorry i don't know the names) then go east to the next city and go to the top of that city behind the last house on the left will be a corridor walk around the house and into a cave, take a left once in the cave and head north until you reach a wall. walk east until you see a guy stop walk around him and don't battle him unless you want to get some xp walk past him to another wall and you'll see a boulder smash it using "rock smash" the you get tri attack Tm.
you cant
In Pokemon I've never heard of that attack Could you mean: Double Kick or Tri attack. If you mean Tri-attack the well: Tri Attack does damage, and has a 20% chance of either paralyzing, freezing or burning the target. Each ailment has a 6.67% chance of being inflicted. The Pokemon that learn it is: Duduo, Dodrio, and all the Porygons! So i think you meant Tri attack.
tri attack is not a TM in platinum. tri attack used to be a TM, and could be found on the roof of the celadon department store, but future generations replaced it.
Magneton can only learn Tri Attack through the Move Relearner in Pastoria City in Pokémon Diamond, Pearl and Platinum.
Level 21
you don't
There is no best level to evolve Magneton into Magnezone as long as it knows Tri Attack before you evolve it if you want it to know Tri Attack because Magnezone cannot learn Tri Attack in any way because other than Magneton learning Tri Attack via the Move Re-learner, their move pools are exactly the same except for a Move Tutor being able to teach Magnezone the Iron Head attack which is a move that Magneton cannot learn.
I don't know soz
yes, when it evolves into dodrio.
its Fairly Decent had the Attack Power of 70 but Flamethrower has 95 and Blizzard has 120 (Just for comparison)
dodrio (evolution of doduo) and magneton (evo of magnemite)
its not a TM but dodtrio can learn it by leveling up.