Dash Procs Luden's now?

it does true damage, not magic damage.

but it deals spell damage because its a spell that deals damage. same reason why spellvamp works on smite.

TD = True Damage? SD = Spell Damage?

What does true damage have to do with anything?

People need to learn how abilities work, this is ridiculous.

The type of damage an ability deals, the stat an ability scales on, and whether an ability applies spell or on-hit effects are completely unrelated. They trend towards certain things, but they are not inherently linked.

1. An ability typically scales on either ATTACK DAMAGE (the stat) or ABILITY POWER (the stat). This does not inherently mean an ability deals magical or physical damage. Lee Sin's E scales on 100% bonus AD and deals magical damage. Miss Fortune's Ult scales on AP and deals physical damage.

2. An ability typically either applies spell effects or on-hit effects. Rarely an ability might have two components that each apply one of them (Fizz's Q, Ekko's E), or might apply neither (typically passive AoE auras or abilities that are, themselves, on-hit effects.)

Mark/Dash is a summoner spell. It deals TRUE DAMAGE, does not scale on anything but champion level, and applies spell effects. Mark applies Rylai's. Mark applies Spellvamp. Mark applies Luden's. The same is true of every summoner spell that deals damage. To sum up, the type of damage an ability deals have absolutely no influence on whether they apply spell effects. What an ability scales on basically no influence on what type of damage it deals. The only thing that determines whether an active or toggled ability applies spell effects is if it is defined to apply spell effects.