Ever had a fever dream? No? Well, now you can, while you're awake, for free... sort of. Monsters Invade: Oz - as in, wizards, not shower shivs - is like being dunked into a vat of LSD. Oz has been invaded by Pokémon - sorry, monsters - and you gotta' catch 'em all inside a magic book. The similarities to Nintendo's classic series are strong. The connection to Baum's classic? Not so much.

You know you're in Oz because there's a yellow road and you're a young girl. Other than that, the comparisons are looser than Microsoft's Xbox One policies. Do you remember that bit in The Wizard of Oz with the igloo and the security cameras? No.

Which is fine - the game is meant to be surrealistic, and taking liberties with source material can work, but sadly these backdrops are just dressing, like the NPCs - you can't interact with any of it.

The actual game part is straightforward. You walk around by tapping the screen, collecting a dozen or so items to unlock the next area, also engaging in random battles. Monsters are coloured, with different colours weak against others. The intricacies of this aren't explained, and it's not immediately apparent; unlike Pokémon's simple elemental system.

Each creature has unique stats, changing as they evolve. Yet, regardless of form, they can only attack. It's a constant cycle of hitting and being hit - no buffs or specials. Attack power is decided by the player's timing. You tap the enemy and a quarter-wheel appears onscreen. Cursors of increasing speeds dart back and forth across it, with the aim of stopping within the green sweet spot three times. If you're successful, a random multiplier will be added to the base damage, with experience handed out for each attack.

Fighting is a simple affair - not a good thing, since it forms the game's core. There are other drawbacks to the system, too; your attacks will miss if timed wrong. Your enemies never miss, however, as their strikes aren't governed by dice rolls. The only form of defence is to heal your creature before its health reaches zero.

Healing is applied with a substance called ink, with costs varying significantly each time. Small amounts can be obtained in your travels, but never enough and eventually you'll run out. When this happens, you must buy it with gold bars - an even rarer resource. Of course, since the game is free, these can be purchased with real money - you can buy a castle's worth of the stuff for £34.99.

It wouldn't be so bad, but you need gold for nearly everything, not just to gain an advantage. The need to keep buying more ink makes using real money inevitable and - potentially - costly. At first, the game seems promising, but it doesn't take long before its limitations become obvious. There's an addictive quality to monster collection, but the game feels more U2 than Mewtwo. You're better off playing Pokémon while reading The Wizard of Oz.

Played for five hours