This guy is kinda broken =/
He's a shamelessly good chaser who can STUN someone with his dash, gets a movement speed bonus after the dash, then his ulti gives him MORE movement speed. If that 30/45 is a flat movement speed bonus and he got boots of swiftness, he would effectively almost have no drawback boots of mobility past level 11.
He would be a broken roamer since his dash and movement speed make him impossible to escape in the right situation.
Edit: Also the fact that the Stun/Dash combo can be used every 8 seconds, most champs are lucky to have a cooldown that low for a dash, and given this guy has Sejuani level lockdown (even better, Sejuani's dash can't potentially stun), I think the dash would only be fair to begin with at about 20-30 or so seconds at level 1.
Then there's the fact his ultimate is 'target anywhere'. This means he can slow people without even zoning them, run in with his massive movement speed, STUN them, and pretty much give them no opportunity to counter. Combined with the fact that the stun combo comes with the original effects of the dagger, that's insane.
Actually I just noticed the Carrion Swarm, two forms of soft CC, BOTH AoEs, can you imagine if Trynd had an AoE slow instead of his single target slow?
Then there's the fact you've given him a base movement speed of 330, the highest in the game...
Flavor wise, great. Mechanic wise? So ridiculously OP it's not funny.