Increase your Tenacity and Slow Resistance for each summoner spell on cooldown. Immediately after casting a Summoner Spell, gain a larger burst of Tenacity and Slow Resistance for a moderate duration.
As Blitz you can easily proc Aftershock to continue fighting. The explosion further assist in kill potential.
WhyDemolish
Demolish on Blitzcrank is great for snowballing early lane picks/kills into meaningful tower damage and early gold advantage.
WhySecond Wind
Second Wind's mid-fight health sustain is great for level 2 all-ins and lane trades where the extra health can be the difference between death or a double kill.
WhyUnflinching
Unflinching on Blitz allows you to stick to your target after hooking them so you can follow up provide extra CC and damage.
WhyBiscuit Delivery
Biscuit Delivery paired with Second Wind and Bone Plating make you a resilient tank in skirmishes as well as allow you to shrug off any incoming poke damage.
WhyCosmic Insight
More CDR from Cosmic Insight means more chances for hooks and teamfight CC with [E].