This build is super annoying!
For the enemy team ;)

Lvl 1: "A fishy deal" - A must have in this build. The talent makes you wander around looking for empty lanes and popping your Pufferfish. At the beginning of the game you have to cast 1 or 2 Slimes to get the full wave worth of "A fishy deal"
Lvl 4: Optionally you can go for "Slime time", but with this build we don't engage that much in team fights in early game, but make sure to pressure lanes during objective times. Living the dream helps you to clear camps faster, if you haven't got "A fishy deal"-bribes available
Lvl 7: The Slime Radius increase offered by "Black Lagoon" is great. Optionally "Time to Krill" could be good for the stacking slowing effect.
Lvl 10: When having obtained "Octo-Grab" you can join teamfights more often and trying to secure kills on overextending/out of position enemy heroes. Make sure your team attacks them when octo-grabed!
Lvl 13: "Fish Tank", which allows you to heal for dmg dealt with basic attacks and abilities, feel like a real power spike! You can comfortably take all non-boss mercenaries with ease and your presence at team fights gets much better. Make sure to pop your Pufferfish, possibly not being able to be destroyed in team fights, so that the dmg dealt heals you as well.
Lvl 16: "Toxic Buildup" is great. It allows you to hunt down left alone heroes faster with every 3rd attack releasing another slime. It is especially good vs mages like Li Ming. Because it is hard for them to hit you at close range.
Lvl 20: The cooldown of Slime is cut in half (!) with "Making Inky", which lets you heal even more often from the Lvl 13 talen "Fish Tank". Mercenaries are cleared very fast!