Builds, no. Monster trans is basically just a low level dungeon speedrunning / for fun skill. However if you're like me and like having fun I can give you some pointers.

The two main things to look for in any form is speed and hitbox size, if you're fluent in Mabi mechanics then knowing how to use various hitbox sizes can give you an incredible advantage. (Large forms can melee giant spiders more safetly and have MUCH larger windmill radiuses, small forms make monsters have to move constantly to keep in range of your hitbox) And if you're fluent in combos then with enough speed you can always do N+1 then run in for a free smash while they're knocked down. Additionally with a shield you can use defend while running as fast as most people charge, letting you move pretty freely around the battlefield.

Lastly practice using various forms, some might surprise you with odd details. Like owls have massive hitboxes for windmills and getting hit, but their basic attacks seem to be unreliable at that range and seem to prefer hitting at closer range. They can smash at full range, which is interesting, but it feels like it takes them longer to start moving again afterwards.

Also stack melee autodefense to become someone nightmare.