For your 2nd ever team, its not a bad attempt. Let me try and help you fix some things up.
Mamoswine @ Chesto Berry
Adamant, ATK 252 SPE 252 - Oblivious
Earthquake
Ice Shard
Stone Edge
Rest
If you are posting Mamoswine first because you are going to be lead with it, don't. Mamoswine doesnt make a great lead. It is a good attempt at something non-standard, but after the first chesto berry is used, then rest becomes pretty much useless as you wont have the bulkyness to take 3 more hits while you wait to wake up.
From the EV Spread, it looks like you want a sweeping Mamoswine, I would recomend changing Rest for Ice Fang and throwing a Choice Band on this mamoswine. Mamoswine also does not need 252 Speed EV's. 192 Speed EV's is enough to outspeed main threats and you can then dump the final 64HP EV's into HP.
If you are looking for a status absorber and want to stick with rest, I would suggest using the Rest-Talk set:
Mamosine@Leftovers
Snow Cloak
Adamant
124 HP / 252 Atk / 64 Def / 68 SpD
~ Earthquake
~ Ice Shard / Avalanche
~ Rest
~ Sleep Talk
Salamence @ Leftovers
Bold, DEF 252 SPE 252 - Intimidate
Roost
Draco Meteor
Flamethrower
Earthquake
You shouldnt really use this salamence as a physical wall since you have a number of other Pokemon which will work much better than Salamence. I would recomend turning him into a sweeper.
Salamence @ Life Orb / Leftovers / Yache Berry
Intimidate
Adamant
120 HP / 252 Atk / 136 Spe
~ Outrage / Dragon Claw
~ Earthquake
~ Fire Blast
~ Dragon Dance
Outrage is really the ultimate salamence attack for late game sweeps and works excellent with Life Orb and after a single dragon dance it can terrorise teams. Dragon Claw works better if you want to have more control over your Pokemon. Earthquake provides nice coverage along with Fire Blast which will help you hit Physical Walls that might try and wall you such as Forretress and Skamory. it also lets you beats Scizor.
Gliscor @ Leftovers
Jolly, ATK 252 SPE 252 - Hyper Cutter
Ice Fang
Thunder Fang
U-turn
Earthquake
You should make Gliscor more bulky and the Pokemon to provide Stealth Rock support.
Use this EV Spread: 252 HP / 12 Atk / 28 Def / 218 Spe. It provides enough speed to outrun adamant lucario and lets you OHKO it with Earthquake. It also gives your Gliscor much more bulky to let it take hits.
For the moveset I would go for:
Earthquake
Ice Fang
Roost
Stealth Rock
Earthquake and Ice give you excellent coverage. Earthquake also gives you STAB damage. Roost is there to recover off lost damage and Stealth Rock to provide your team with the rocks. Either Ability works but maybe Sand Veil would work slightly more in your favour as sandstorm is very common.
Zapdos @ Leftovers
Timid, HP 252 160 SPD 96 SPE - Pressure
Roost
Toxic
Thunderbolt
Substitute
This set works fine. If you can get Baton Pass for a Zapdos, then you could consider that to pass Substitutes. Hidden Power [GRASS] could also provide somewhat useful to beat Swampert and hit ground types that will resist thunderbolt. Your team could struggle against some forms of Swampert as you lack a real counter but you can wear it down with Suicune, or explode with Heatran if its providing to be a real nuisance.
Heatran @ Choice Scarf
Timid, SPA 252 SPE 252 - Flash Fire
Earth Power
Fire Blast
Stealth Rock
Explode
Looks pretty strong. You can drop Stealth Rock if you give stealth rock to gliscor. This will make room for another attack. Hidden Power [ICE] will provide the best coverage. If you cannot get Hidden Power [ICE] then Dragon Pulse is the next best thing. Beware that Dragon Pulse cannot OHKO Dragonite even with Stealth Rock support and you only have a % Chance to OHKO Salamence after Stealth Rock damage. Dragon Pulse will help beat Kingdra better than Hidden Power [ICE] however.
You have 6 EV's spare, Slap them onto HP. that one extra point could be vital.
Suicune @ Leftovers
Bold, HP 252 DEF 252 - Pressure
Ice Beam
Surf
Mirror Coat
Reflect
Use the final 6 EV's and put them into Special Attack. At a glance, Gyarados could become a huge problem if you let it Dragon Dance. Suicune can counter it very well as long as you have got Hidden Power [Electr]. I would suggest giving it Hidden Power [Electr] to tackle Gyarados and so you can hit other bulky waters that might try to come in and wall you. I would also use Calm Mind somewhere in there too if I was you so you can calm mind up against non-threatening Pokemon and then start to sweep. Suicune really doesnt need Mirror Coat, so you can drop this for Calm Mind. I would then drop Reflect for Hidden Power [Electr]. You also have quite alot of Ice attacks throughout your team, and you will have even more-so if you take any of my advice so it could be an option to drop Ice Beam and you could give it roar to stop baton passer and just to shuffle your teams Pokemon around while damageing them through Stealth Rocks.
~ ~ ~ ~ ~ ~
You have done a pretty good job with team, although it might be standard, it has promise. You need to fix some of the sets and spreads up like I mentioned. Once you have improved the sets and spreads, yo can then start to look at the main threats that would threaten your team and then work to tackle the MAIN threats. You shouldnt look to tackle alot a little threats as then your team will create gaps and could become weak to big threats.
