Ogre magi needs fireblast whole game, and mostly on mid/late. By the way, even getting 4x multicast isn't enough in my opinion. It does a big damage when hits 4x, but it could be better once Aggron is one of the heroes "heaven or hell" in the game. It's hard to hit multicast always, and right, it must be hard. After all, it does needs a upgrade by Aghanim's Scepter. I thought that it could be fair if before add more % on multicast or even more multicast, it add damage per multicast:
Let's say I hit 2x multicast with ultimate level 3 and fireblast level 4.
The damage will be 550.
It's ofc a nice damage for only 2x multicast, but on late game it doesn't even help if you get 2 or 3 multicast.
I'm up to suggest a Aghanim upgrade by doing the same thing as Aggron is in the game, the "heaven or hell". So it could be:
Normal cast: 285.
2x multicast: frist cast doing 285 damage, second doing 310 = 585
3x multicast: the same as up but in the order: 285, 310 and 360 = 955
4x multicast: 285, 310, 360, 460 = 1415
Normal cast: 275
The order of upgrade in damage that I used was:
1x = 10
2x = 10 + 25
3x = 10 + (25 * 2)
4x = 10 + (25 * 4)
About ignate I would say: add more damage. I really don't mind about ignate and if my suggest is good I prefer let someone else think on it for me.
About Bloodlust: 100% chance to multicast 2x and upgrade multicast % on 3x and 4x.