Core Fusion must be done via the workbench in your crawler. From there:
• Corebot must be max level (30)
• You must upgrade all 3 stats (Attack, Defense, Energy)
• I used Mack, and at level 30, his max stats are: 280 - 380 - 480
• Duncan: 480 - 280 - 380
• Seth: 380 - 480 - 280
(interesting trifecta of max stats...)
This will use quite a bit of fusion materials, and you can upgrade faster by holding down
. Not sure why they couldn't make this faster, complete oversight on the developer's part.
You can use any of the three bots. NOTE: As suggested in the comments, it is recommended to upgrade Duncan first, as he has the highest attack and his area of effect (AoE) lethal is fantastic for clearing groups.