The phrase "deadly slow" is grammatically correct and can be used in written English.
It is typically used to describe something that is extremely slow or painfully slow. You can use it when describing a situation, object, or person that is moving or working at an exceptionally slow pace. Example: The internet at the hotel was deadly slow, making it nearly impossible to get any work done.
The rest of that summer was deadly slow.
The highlight of the performance is a deadly slow cover of the Grateful Dead's Easy Wind.
When the first Eye-Fi SD cards came out, they were impressive (wirelessly uploading photos from your camera to your PC and online photo sites) but deadly slow.
In fact, TC progress remains deadly slow in several European countries such as Portugal [ 3, 6].
England soon realised that wicket-to-wicket hustle was Kumble's modus operandi, and he was deadly on slow, low wickets even before DRS. In the end England had 21 problems with him, each at an average of 19.80.
When Jack is exposed to the deadly but slow-acting Nyodene D, the abstraction of his death becomes concrete, prompting an existential crisis that propels the novel towards its violent ending.
If the wantonly negligent operation of the school led to many deaths, the Florida School of Boys was like a deadly fire in slow motion.
Then, stand behind them and throw a Venom Cask directly on top of them (adding 2 stacks of Deadly Venom) to slow them and then attack until you have reached full stacks of Deadly Venom on your opponent when you will Contaminate to add some additional damage output.
In fact I'm on a wild island, with an invasive species far more deadly than the slew of cruise ship passengers meandering around the myriad duty-free stores in the capital Oranjestad.
The degenerative and ultimately deadly disorder had slowed him down, he told the students, but life is too short to not steal a Krispy Kreme truck.
Venom cask: Twitch hurls a cask of venom at an area, infecting struck enemies with 2 stacks of Deadly Venom and slowing them for 3 seconds.
