A quick collection of tips for Gambit - Prime and normal.
A lot of people suck at Gambit. Sorry if you are of those people, but in so many public matches people seem to keep making the most basic mistakes. I don't think Gambit is hard (it really isn't), but there are a few tricks worth knowing. Here are some of them.
(This guide is intended for people very new to Gambit, or those who just don't understand how some of it works. I've left out the Gambit Prime armour sets as other than the Collector set, the rest don't hold much weight over games.)
Prime vs. Normal - The Basics
Let's start with normal Gambit.
You clear crowds of mobs, and need to bank a total of 75 Motes to spawn your Primeval. Once it spawns, 2 additional Wizards will spawn alongside it. KILL THESE WIZARDS BEFORE DOING DAMAGE. In order to do damage to the Primeval in normal Gambit, you must get a stack of buffs called "Primeval Slayer". You get one stack per Wizard killed (the 2 that spawn with the Primeval) and an additional stack every 15-20 seconds. Once you reach 4x stacks, you can begin doing decent damage - and if your team is good enough you can kill it at this point if not at 3x stacks.
Now Gambit Prime.
Prime shares the same basics and normal, but with a few notable twists. The first being that you need 100 motes instead of 75, and blockers can now drain Motes if 2 or more are present at your bank. Keep your bank clear, and you can make it to the Primeval with ease. Dealing damage to it however is different.
The Primeval will spawn with a shield around it that cannot be broken. Once it spawns, 2 Wizards will spawn somewhere on the map, next to each other. Kill both of them, and a final Wizard will spawn near the boss. Kill this Wizard to THEN begin the damage phase - which lasts 30 seconds. Each full rotation of what is listed above grants 1x stack of Primeval Slayer. This buff is given to you in the form of a white circle on the ground. You CANNOT AND WILL NOT do damage without receiving this buff. If your team is well-coordinated, you can melt the Primeval with 2x stacks easily - 3x to be safe.
Clearing Enemies, Collecting, Banking and Blockers
Clearing mobs is the basis of Gambit - they drop Motes. Killing enemies quickly and efficiently is the key to Gambit. Saving your Super for an Invader to then one-shot you is kind of a waste, so always pick supers suited for clearing crowds. Tether for Hunter, most of Warlock's supers and Titan's Hammers are usually best for this.
Collecting Motes is THE most important part of Gambit. But contrary to popular belief, getting 15 Motes is throwing the match for your team. PLEASE STOP GOING FOR 15 MOTES. The large blocker is objectively the worst of the three blockers.
The small blocker (5-9 Motes) can make other blockers invincible - including other small blockers; the medium blocker (10-14 Motes) tele-ports a lot and can be a pain to deal with; the large blocker is just a health pool. Let's say your team is at 88 motes in Gambit Prime, and you have 13. If instead of immediately banking them, you go and get another 2, you have just cost the match for your team. Because right around that threshold, if an Invader rocks up and beams you, he just bought the enemy team time to get their Primeval up and you just lost a very substantial amount of Motes.
Stop only going for 15 motes for the love of god.
Lastly, blockers. For the love of all thats *** holy, prioritise blockers. As their name suggests, they block the bank - making it impossible to bank motes and opening you to an invade from the enemy team. Blocker take priority over everything else in Gambit, besides an Invader. Doesn't matter if you need 1 more Mote, or there's a heavy ammo brick lying on the ground, blockers come first.
Invading, and Dealing with Invaders
It is debatable that this is the easiest part of Gambit. Even if you've solo-queued for a quick game, this is often easier than anything to do with Motes.
A lot of people think that an Invader is too strong, like it's unfair to fight them. But when you think about it, it's very much the other way around. The Invader has chosen to fight what is essentially a normal PVP 4v1 fight. Thus him being able to see you through walls is fully justified. Dealing with an Invader is quite simple: heavy ammo. Just like normal PVP, heavy ammo is they key to free kills. The only heavy weapon class not suited to Gambit are swords. Everything else can be used to good effect, it just depends on your knowledge of invasion spawns and map awareness.
To be a good Invader is a bit harder. As much as people like to joke about an Invader running in with super or heavy ammo and wiping your team being brainless is funny, it's also completely understandable. You're going into a 1v4, and its quite possible all of them have heavy ammo on-hand or sniper rifles. If you want to be an Invader, solo-queue or pre-lobbied, don't just rush into people. Getting one kill and being destroyed isn't helping your team at all. Take your time, and make your shots count. You really don't need to get 4 kills every invade to be 'good enough'. A couple 2 or 3 kills help a LOT more than getting 1 full team wipe and never getting more than one kill every other time.
Kill, collect, clear, bank and win. It doesn't need to be that hard. Just play the objectives right and you'll roll lobbies. Get to it Dredgens!