isa helps lavos

Checks VS:

Snorlax - try to scout its moveset with Skarmory/Suicune. If you have Forretress in, use Toxic BUT ONLY IF YOU HAVE CONFIRMED IT TO NOT BE A FIRELAX (or if you know guaranteed that your opponent has no way to remove/set spikes after Forry dies). If Snorlax comes in on Raikou you can use Thunder once before switching out (assuming high HP raikou and snorlax), it'll hurt him a lot if he turns out to be a drummer
CurseQuake - Skarmory
CurseFire - Gengar (hit it with Hypnosis then try to make it GTFO with phazing or your own Lax), Raikou can phaze if it's in to prevent cursing
DrumQuake - Skarmory
DrumFire - Skarmory, Gengar (skarm takes about as much damage from return as fire blast at this point so it's all good).
Three attacks + Rest - Suicune uses Toxic and stalls ez.
Raikou - This is an issue - your own Raikou is your best response to opposing Raikous and you can't paralyze him reliably due to TBolt, so you'll be forced to Rest. Snorlax can come in on predicted non-Thunders and threaten a Drum but if you take a Thunder (esp with spikes on your side) drumming is out of the question until you've gone up to 90%+ again.
Zapdos - Not an issue. Raikou wins easily, Snorlax can come in. Gengar does damage with Ice Punch but you don't wanna switch in Gengar because of that.
Cloyster - Forretress can't really come in on Cloyster as it takes a lot of damage from Surf (3HKO). If your Forry comes in before though, you can toxic it easily and secure spikes in the long run. Post-Spikes, use Raikou as a check as long as you predict him not to explode (also remember that RSpin + Explosion is illegal on Cloyster), once he gets into low HP ranges use Gengar more liberally.
Exeggutor - Raikou is a general check, Suicune wants to be the sleep taker though. If it lacks Giga Drain, Suicune beats it, if it lacks HP Fire Skarmory and Forretress beats it. If it uses Leech Seed, go to Forretress if you need to do something revolving around Spikes (again, check for HP Fire), otherwise Skarmory is fine here.
Gengar - Raikou is the premier Gengar check. However, Explosion commonly catches Raikou and if your opponent has a sweeper that wants Raikou gone (Vaporeon for example) this can be abused by your opponent. Keep him honest by employing Snorlax as your switchin every now and then.
Miltank - Gengar obviously cockblocks. If Miltank comes in on your Snorlax, free drum. Skarmory can come in as well but doesn't really do anything, Raikou can come in and do some damage with TBolt.
Nidoking - Suicune is the best check you get, check damage calcs. Speed tie though. Once Sleep is thrown you can use Snorlax more liberally. Forretress doesn't really do anything vs. Nidoking but you can use the time to play the spikes game and then go suicune/lax.
Skarmory - Raikou obv. destroys it. Snorlax deals ~40% after lefties when drumming. Suicune, similar amounts with Surf. Gengar forces Skarm out. Switch in Raikou to play the spikes-roar game is my general advice but beware of Skarm suddenly shuffling you.
Starmie - Forretress wins 1v1 as long as Forretress was in from the beginning, so you should have no issues keeping spikes down. Just use HP Bug, ~60% damage before lefties. Otherwise, Raikou/Snorlax/Suicune all come in without any issues. Gengar lives a Psychic but you really don't wanna go there, and Explosion isn't even a guaranteed KO.
Steelix - Suicune blows it out of the water. A "common" strategy that Steelixes can employ is that +1 Steelix has a guaranteed OHKO with Explosion onto Suicune, and Suicune's Surf does not OHKO Steelix, but it's still your best general bet by a wide margin. DrumLax doesn't OHKO either with Earthquake for what it is worth - check calcs if it has taken minor damage though because it is incredibly close.
Suicune - Your own Suicune is always safe vs. opposing Suicunes. Raikou can come in but you don't want to take a Toxic if it can be avoided. Snorlax does not OHKO with a Drummed Return either, but the only counterplay is Surf/Roar so yeah.
Tyranitar - Suicune is almost always the best option you will get regardless of variant. Raikou can at least deal some damage to variants without Earthquake without risking its life and Snorlax can handle TTars that aren't cursing or DynamicPunching, but as said, Suicune is the best bet.
Vaporeon - if it's a STalker (which most but far from all are), Raikou is your best bet. Snorlax OHKOs if it drums, but if Vaporeon uses Growth on the switch to Snorlax, you cannot drum and will lose. Gengar can explode or use Thunderbolt as a second look.
Blissey - FREE DRUMS. You can play the spikes game vs. it as well, but beware of Flamethrower. Gengar can come in and threaten a Hypnosis, but you shouldn't do that unless you've confirmed that the opposing Lax is not using EQ.
Dragonite - if it's the defensive variant, you can Drum fairly freely and get some damage here and there, but you're better off using the time to set up spikes or threaten it with Raikou. If it is the offensive variant (Thunder/DynamicPunch/Double-Edge/Ice Beam are common moves), Raikou is your best bet. Gengar can work as well if you get it in on a move that is not Thunder. (Dragonite does not get Earthquake.)
Forretress - if you are low on HP, you can always stalemate with your own Forretress. Gengar ALWAYS prevents the spin vs. Forretress (nobody runs HP Ghost Forretress) if you wanna block Rapid Spin at once, and is also good at applying offensive pressure. Suicune's Surf deals damage, so does Raikou's Thunderbolt.
Heracross - Skarmory is always super safe (Curse+Counter can screw with you though, albeit incredibly rare). Gengar takes ~15% from Megahorn before Leftovers. If he uses Earthquake though then you take ~75%. You can set up spikes, Toxic and then switch out if you wish.
Machamp - Skarmory can phaze it unless you get lolcritted. Suicune is 3HKOd by +1 Cross Chop (without Spikes) but 4HKOs back. Gengar doesn't take anything from Cross Chop and you can use him as part of a chain switch to get something in safely (or stall Toxic damage if it comes to that), and is 3HKOd by +1 Rock Slide. Don't try to fight back though with Gengar (bar Hypnosis maybe - again, depends on scouted Lax set). Apply offensive pressure on it to beat it. If it Resttalks - BEWARE OF PURSUIT TTAR IN THE WINGS, but use Gengar to completely wall Champ still.
Marowak - Skarmory and Suicune = supposedly unbreakable core here, although Surf does not OHKO Marowak. Thiefing away Thick Club means that Marowak is super worthless. Spikes will limit the number of switches given.
Misdreavus - Raikou is better than Skarmory at checking Misdreavus - you don't want to be Thunder weak. If it is Confuse Ray, you can go Skarmory though if you so please (reduces possible Spikes damage).
Rhydon - Suicune is the best thing in stock here. Surf OHKOs easily. Snorlax doesn't like this despite having Earthquake.
Umbreon - until you can be sure this is not Baton Pass/Mean Look, use Skarmory (or Raikou) AT ONCE. Consider every unscouted Umbreon set a potential Passer. If it turns out to be using Charm/Toxic/Pursuit/Recovery though, this is not a threat. Forretress comes in for free, Snorlax can drum on it without much fear (Toxic is the most threatening), Skarmory is Toxic immune and can Thief/phaze, Suicune can Toxic. This thing is generally defeated through Toxic, but if you can break it with Drum that works as well.
Charizard - Gengar and Raikou outspeed, but only Raikou OHKOs with Thunderbolt after a Drum. Snorlax lives +6 Earthquake guaranteed (as you know) and so does Suicune, who OHKOs post-Drum.
Clefable - Toxic destroys it if you can get it safely. If it carries Fire Blast, Gengar disregards it. If it carries HP Ground, it doesn't break Skarmory. Forretress is 3HKOd by Return, which means that you can get a desperate Toxic on if you need extra damage badly.