Here's some advice for getting a streak of 10 in I, Zombie Endless:
1. Use your Sun wisely, if you start the first match and there isn't a lot of Sunflowers in the lawn, keep restarting until you get a lawn with lots of easy to get sunflowers, use the Imps to eat the ones right in front of the lawn, since they're cheap and you'll get lots of sun in return
2. Keep an eye out on 3 specific plants: Threepeaters, Magent Shrooms and Starfruits
-My best advice is:
A) Quickly spawn 2 Coneheads one after the other, that way, one of the Conheads will be a meat shield for the other, making you clean the lanes very quickly, do this strategy on lanes with both Threepeaters and Starfruits, as well as Kernel Pults who can also give you trouble.
B) Use the Bungee Zombie to steal the Magnet Shroom, since it can counter most of your Zombies, just make sure it's not close to a Umbrella Leaf, if there is one nearby, use Double Conehead or Imp depending on the situation
3. Now for the Zombies and what they can do:
Imps - They are cheap but extremely weak, only being able to survive a single Spikeweed, but they can be good for getting rid of Instakills like Chompers or Potato Mines and are very quick, so they can eat the brains with ease
Coneheads - These guys will help out a lot, they have decent health, are cheap and are not affected by Magnet Shrooms, use the Double Conehead strategy and you will clean lanes pretty fast
Pole Vault Zombies - They are fast and cheap, but have less health then a Conehead Zombie, they can be useful for Kernel Pults and Wallnuts but be careful, because they can also jump over the Sunflowers
Buckethead Zombies - You won't use him often, he's pretty slow which makes him not good for lanes with Snow Peas, he's a bit more expensive and while he does have more health then 2 Coneheads, it's still best to use the Conehead instead. Only use him for medium difficulty lanes
Bungee Zombies: You'll mainly use him for Magnet Shrooms and for any Threepeater or Starfruit that is giving you trouble, just be careful with the Umbrella Leafs, since he's pretty expensive for what he does
Digger Zombie: He's great for clearing lanes, but he usually needs to be paired with a Imp or Conehead Zombie. Just don't use him in lanes that have Squashes, Potato Mines or Split Peas
Ladder Zombies - He's not useful for his climbing but for his defense, he can be a tank thanks to the ladder that works as a shield, which is useful for Snow Peas
Football Zombie - Not much to say about him, he's good at clearing lanes and has pretty good health, so if you can't use a Digger Zombie, use him
Dancing Zombie - He's the most expensive and is not the most useful, but in situations with lots of Instakills, he's pretty handy and is actually cheaper then using a bunch of Imps, since he can summon an infinite amount of Zombies to back him up and eat 3 lanes at once, he doesn't have a lot of health though, so use him wisely
Lastly, there's 2 specific scenarios that might end many runs, those being lawns with lots Starfruits and Spikeweeds, and lawns with lots of Magnet Shrooms and Fume Shrooms, here's some advice on how to finish those:
Starfruit + Spikeweed - Simply use either Coneheads, Bucket Zombies or Footballs Zombies depending on how much they can take, make sure to get rid of all Starfruits before anything else
Magnet Shroom + Fume Shroom - There's not a whole lot you can do with this layout, your best bet is to spam Conehead Zombies or maybe even Pole Vaulting Zombies, you WILL lose lots of sun in this layout, so make sure you have a lot of sun in case this layout comes up. If you're lucky, you might even get the Scaredy Shroom and Sunflower combo which is a huge game changer!
Good luck! You'll need it!