I tried calculating the stats for this fusion and they're a little different than I expected.
First I'll discuss the method. Calyrex's fusions actually have a very, very simple way of calculating stats: HP doesn't change from base form, and non-HP stats are just (mount's base stat)+20. This is why Calyrex-Ice's Speed (50) drops by 30 compared to base Calyrex (80), it's just +20 to Glastrier's Speed (30). So by following the same method we can just take Chi-Yu's HP, Lando-T's base stats, and then add +20 wherever needed. That gives us...
55 HP, 165 Atk, 110 Def, 125 SpA, 100 SpD, and 111 Speed. This comes out to, and I am not joking here, a 666 BST. Incredible. Arguably it could be faster because the reins are a Choice Scarf.
Ability would obviously just be a variant of As One (Beads of Ruin + Intimidate). Typing would probably be Dark/Ground because Calyrex foregoes its secondary type for the primary type of its mount. Not great in terms of weaknesses, as you're vulnerable to Fighting, Fairy, Bug, Ice, Water, and Grass. Good STAB combo though as you're hitting 97% of known species for at least neutral damage. It's probably got a good Rock move or two to smack Yveltal with at least.
