Note: If you do not have a second controller you can boost these online as well
Plug in a second controller, and from the main menu go to multiplayer>offline. For your character pick Godric and for his soldiers pick any combination of spearsman and swordsman, no elite or champion units. For the second controller pick anything.
When the game starts evaluate your troops. See which troop color (soldiers and spearman) you have the most of. Now you will be going for Sir-Links-a-Lot first. Try to get a column (up and down) of units in this order if say you have a lot of white (front to back). White-Yellow-White-White. Or flipped with 2 Whites, then a yellow, then a white. You should have 1, 2, or 3 of these already made from the start if you are lucky.
Now the most important thing to remember is to not make walls on accident. To avoid this you can do two columns of the formation, then a blank column, two more, a blank column, then the last column of this pattern. You probably will not have 15 of one color unit to start with, but that is fine. Delete all other units that you do not need and eventually re-enforcements will bring a unit color you need. When it is the second controller’s turn, just end your turn (x) or delete 3 units (for fun). Eventually you will have 5 patterns like the one I described earlier set up, when this happens, delete the unit in the center (in this case the yellow) and repeat for the other 4. Be carefully to not get trigger happy and delete a White one like I did, because then it is time to retry. After all 5 of them link the achievement should unlock.
Now for Fusion Fanatic, the reason you have swordsman and spearman is because they have a charge time of 3 turns, plenty of time for 2 fusions. First get 9 of the same color units so that you can easily move them without moving other units. Delete an entire column of units and put an attack formation of the color you have 9 units of. On your next turn put 3 more behind the attack formation, and then repeat on your next turn. Once your 2nd fusion takes place, the achievement will pop. You can do this in the same game as Sir-Links-a-Lot.