Daemons you say? This should be a cake walk. Spoiler: it was. The pictures are pretty bad here so you'll have to excuse me and the game isn't exactly that fun but it does highlight some key things. Like how poorly Daemons matchup against a 5th edition army. Let's start from the beginning then and I'll try to keep this brief. Mission was Table Quarters, Objectives, Kill Points.
Game 6 was against Simon Rainbow who helped provide some of the terrain. I will need to talk him it seems! He played Michael Cruise (the Footdar) in Round 5 which make my Game 4 loss even more hurtful. No offense to Simon but I would have had an easy Game 5 and be sitting in the final for Game 6. Ah well, that's what I get for playing poorly! I cannot remember the upgrades Simon took on his units but there was not shooting and everything was Slannesh themed with the basic outline being something like this:
4x Heralds
3x5x Fiends w/Might
5x8 Daemonettes
1x 5x Seekers
3x Daemon Prince
There were some upgrades (like Transfixing Gaze on most things) but none of them really came into play. I won the roll-off and gave Simon first turn so I would get maximum shooting. He split his army up basically in equal halves with the Seekers, 2 Fiend squads and a single DP coming down in the first wave. He obviously didn't deploy anything whilst I strung out my two large Strike Squads + Libby to push him back and give me some room to manoeuvre.
Deployment:
Daemons Turn 1:
Simon got his preferred wave in and dropped everything in the back right corner. This was a mistake and something he did against Michael as well. Whilst dropping closer to me would have been more risky (his scatter rolls T1 were huge) and put him in range of all of my firepower, (he was in range of most of my army throughout the game anyway) he'd have threatened me with more units. As it was I was able to focus fire on the closest units and not care about the things farther back even with their potential 24" movement. If Simon had dropped agressively against me (especially considering I didn't have Warp Quake up at this time), I'd have had more than just one or two units I had to kill each turn and put me under more pressure.
With his wave in and no one mishapping, everyone ran so they were in terrain. Everything was pretty much in the top right except one Daemon Prince who had scattered into the bottom right corner. No damage was taken from terrain.
Grey Knights Turn 1:
With Simon deploying passively all I had to do was manage my 24" against one or two units, kill those units and I was safe all game long. Without any shooting combined with the passive deployment, that's all I had to do all game and I was home free. Whilst I was certainly better in combat against Daemons than against many other opponents since I always struck first (even though we forgot about this) and re-rolled hits, I was much better off shooting him so I was happy to be in this situation.
With this in mind I moved all of my units on and disembarked the infantry. The Grey Knights were obviously the closest units with the Razorbacks and Dreadnoughts further back. Both the large Strike Squads moved laterally to get into range but forgot to cast Warp Quake. On the right where the Daemon Prince was I moved on a Purifier Razorback (who walked on), the Chimera with Inquisitor + MM Servitors and a Rhino with which I blocked the path to the Purifiers + tanks.
In my shooting phase I killed the Daemon Prince with lucky dice and dropped the closest Fiend squad to roughly half strength. They went to ground but most of my Grey Knights were only in range of them so I continued to shoot them. The Psybacks + Dreadnoughts took down some Daemonettes and wounded a Herald. These guys were really important throughout the battle not for their extra range but because I'd often use a Psyback's shooting first to get a grasp on the range differences to my back units. I'd then shoot my furthest 24" unit and move forward allowing me to maximise my firepower and minimise how many units would ever be out of range.
Daemons Turn 2:
Not much came down for Simon on Turn 2 (a Herald and Daemon Prince) so he had to make do with what he had. His right flank of the weakened Daemonettes, Fiends and Seekers moved up to assault my blocking Rhino whilst everything else moved forward whilst trying to maintain cover. The Fiend squad which had gone to ground stayed where it was shockingly.
In the assault phase the combined assault of the Daemonettes, Fiends and Seekers did little to the Rhino but stunned it immobilised it for next assault phase.
Grey Knights Turn 2:
With nothing of my main force being pressured again I moved everything up to bring more 24" firepower to bear. The Razorbacks and Dreadnoughts repositioned for better firing lanes whilst the Purifiers retreated on the right to ensure they weren't assaulted next turn. The Chimera moved up to assist this whilst not blocking their LoS and the Razorback moved 6" to be able to shoot whilst not being easy meat in combat.
In shooting I was able to finish off the weakened Fiend and Daemonette squad and dropped the Seeker squad on the right to a single member. Further firepower dropped the Fiend squad on the right to three members and the Psybacks + Psyfledreads were able to kill the wounded Herald and wound the newly arrived Daemon Prince on the far right flank. I remembered to cast Warp Quake this turn but it didn't look like Simon was ever going to DS near me anyway.
Daemons Turn 3:
More reinforcements arrived this time around for Simon with the remaining Daemon Prince arriving and Daemonettes. He placed most of these on the far right where most of my army couldn't see them and he had a numbers advantage. Everything else moves forward but is still outside of charge range.
On the right the Fiends + Seeker are able to destroy the Chimera with the Inquisitor + Servitors being pinned as they exited the flaming ruin.
Grey Knights Turn 3:
Don't have pictures for this turn of mine sorry. Once again I moved my firepower up with my Razorbacks and Dreadnoughts moving to clear fire lanes. The remaining Rhino moves up to protect my Strike Squads from potential assaults and I open fire.
I'm able to drop the wounded Daemon Prince on the right and put a couple of wounds on the remaining Prince. The Psybacks + Dreadnoughts drop the final Heralds and the Purifiers + Razorback on the left are able to kill a few Daemonettes. We head into Turn 4 with the whole Grey Knight army pretty much in-tact.
Daemons Turn 4:
Simon's final squad, Fiends, comes down and lands in the far top left quarter to try and hold that whilst everything else moves towards me. He is finally able to get off multiple charges with some good fleet rolls. The two Daemonette squads in the bottom right multi-assault the Inquisitor + Razorback whilst the final Daemonette squad + wounded Daemon Prince assault the Rhino. The weakened Fiend squad is able to swing around the Rhino and assault the full Strike Squad but thanks to Sanctuary (we forgot psykout grenades) and preferred enemy, died before they could attack. The Inquisitor + Servitors were wiped out and the Rhino shaken.
Grey Knights Turn 4:
The shaken Rhino doesn't bother with Fortitude and moves 12" out of the way to clear my shooting lanes towards the Daemonettes and Daemon Prince. With some urging from Simon I decide not to kill the Daemon Prince with shooting (i.e. I don't shoot the Strike Squad at point blank range but rather just charge) for an epic duel! Many of the small squads down the bottom move to the table edge to get some LoS to the Daemonettes on the right whilst the Razorbacks, Dreadnoughts and remaining large Strike Squad move to get LoS to the Fiend squad in the top left corner.
My shooting quickly kills the Daemonettes with the Daemon Prince so everything else which was going to shoot there shoots the Fiends and kills two. The small squads down the bottom shoot the Daemonettes on the right and halve both squads. In assault the Strike Squad is able to take two wounds off the Daemon Prince who kills two in return. Combat is tied and we go to Turn 5.
Daemons Turn 5:
We were pretty much wrapping up by this point and starting to pack up the event but we had to finish our game! The Daemonettes on the right scartched away at the Razorback but were unable to kill it whilst the Daemon Prince (we forgot psykouts again) killed three Strike Squad members before dying who consolidated towards the Daemonettes. The weakened Fiends attempted to charge the Strike squad in the centre but Sanctuary stopped them and left them in front of the guns of most of the Grey Knight Forces.
Grey Knights Turn 5:
Enter mop-up phase! A combined hail of psy-enhanced firepower and storm bolter shots eliminated both the Fiend and final Daemonette squads leaving just one squad left which had come down last turn in Simon's original quarter saving him from the wipe-out. We didn't bother to roll for game end and called it here.
Conclusion
This was always very likely going to be a one-sided affair and with Simon playing passively, it was pretty much guaranteed unless dice took over. I was able to focus my fire on a couple units a turn with the majority of my firepower and eliminate them. By deploying away from me I was able to do this without fear of reprisal and it basically became a turkey shoot as I didn't have to care about movement. By using a longer-ranged weapon early I was able to maximise my shorter ranged weapons and ensure I never choose out of range targets. Using a couple of vehicles as movement blockers also stopped most of the assaults Simon was able to launch and we saw how well that worked.
Ultimately this had nothing to do with Grey Knight special rules winning the day against Daemons but effective management of the 24" bubble between our armies, tanks as assault blockers and a lack of aggression or shooting from the Daemon side.
It was a nice way to finish the tournament, though one had to feel bad for Simon, though of course there were those questions of what if? in terms of playing Simon in Round 5 if I had won Game 4. Ah well, hindsight :P.