The game has just been released as a demo and people have already found ways to beat the AI in a skirmish 100% of the time, whatever difficulty. Myself included. This guide is my way of defeating the Covenant in under 5 minutes. Its called 'Elephant Rushing'. Someone has found this before me, but mine is a variation of his stratagey.
As soon as the skirmish starts build an elephant via your main base. Whilst that is being built, build 4 Supply drops so you have a steady supply of reasources. Just send your warthog off to collect supplies from around the map, or just leave it where it is if you want. Now as soon as your elephant is built send it to the Covenant base and depoly it as a secondary base, making sure at least two of the Elephants guns can aim at the Covanenants base (The other is for The Prophet of Regret). When the elephant deploys just keep a constant supply of marines and start attacking the base. If any enimies are there, then have your warthog ram them down or deploy some Flamethrowers. Keep doing this and as soon as the base's life get into the red zone, have all of your marines throw grenades at the base to destroy it and if your warthog or flamethrowers have taken out all Covenant units, you will win!
It took me 4 minutes and 43 seconds to win in a normal difficulty skirmish and I have tried it in all three demo difficulties and it works in them too.
Linear Mode
