if the part is willing, experience points can be shared. the party will be taking a pay cut in exp but any hireling, companion or other gains that and takes up the appropriate buffs and bonuses. even training periods can be given to the individual or party to gain exp and catch up, rules are in the Dmg and plenty of named folk in the dnd community have written up official looking guides/homebrew for such a thing. though if you play by milestone, give the same buffs and bonuses to the npc/creature that you give to the party. other than that, go with your gut

Totally starting my one of my players off with this beautiful creature for the start of my waterdeep dragon heist campaign. I wrote in the backstory for the character that this is a friends dog who unfortunately the friend passed away but he gave the dog to the halfling character. I’m making it unique so that each day he rolls a d20. If he rolls a 10 or below the dog doesn’t want to go with the character that day. A 11 or higher means that the dog will be a faithful companion that day

You know what's a crime a mastiff has a seven for charisma it should have at least ten 

I'm using mastiff stats for a wolf dog, whom I named Wyrm. Deathly afraid of mimics.

I believe it depends on your opinion to be honest. Me and my friend owned wolves once which learned and trained between sessions

One was pulled out of a hat and my character took its face in her hands and went "Your name is Bork now" while everyone in my party groaned

Can you put armor on one?

Was recently given Inspiration to make a halfling fighter/cavalier, using one of these guys as a mount. One day I'll try it

I have a level 3 barbarian jackalope who will be using one to carry her pack. It will be great.

Quote from Kydric_Bane >>

Quote from Korgex12 >>

dog

 

Yes, on PHB section "Mounts and Vehicles" it explains how it works to put armor on mounts:

https://www.dndbeyond.com/sources/phb/equipment#MountsandVehicles

GOOD BOY

Shouldn't this thing have more like 30 hitpoints if it's to serve as a war dog?

Get your Druid to Awaken it.  10 Int and it can speak one language.
A talking dog

Depends on what your dm says

do mastiffs level ups tuff?  what if im lvl 10 does he also get skill increases or a feat?

I made my players fight one when they got a nat 20 to tame it and now it follows them

I cannot wait to get a Mastiff. Im playing a small Tabaxi Arcane Trickster with the summon spell of a rat. Cant wait to picture a mouse riding a cat riding a dog.

My party found a mastiff traveling with a bunch of hobgoblin. We killed all the hobgoblins then I cut off a leg from one to tame the mastiff.

My character is getting one of these but it’s going to be a puppy