Just watched the first few minutes here. Everyone is right. 
Couple of reasons Caldarius looks squishy early on here:
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He is. Caldarius’ greatest strength is mobility. He is designed to be very effective at hit and run. He’s not a stand toe-to-toe and fight kind of character. At later levels, his mobility is increased (dash distance, better double-jump, his ULT which is a huge jetpack move).
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This guys wasn’t playing him as hit-and-run. One of the main things the player in this video didn’t do that I see all the great Caldarius players do is use the double-jump. Caldarius gets double-jump at first level. Actually, Double-jump is a bit of a misnomer. It’s a secondary thrust. You jump, and then can thrust (gundam-style) in any direction. Up, down, forward, back. left , right. It both improves your movements speed AND makes it nearly impossible for enemies to land hits on you.
IF you’re going to use Caldarius’ sword, it’s pretty essential that you remember hit and run… Dash in, sword swing at the end, then double jump away. Even that is fairly risky until you have some levels on you and can power up some of those key moves.
Let me assure you though. Caldarius is DEVASTATING in the right hands.
wouldn’t surprise me if he was a robot tho 


