The top two game apps on iOS android that use a crossbow are Defender II and Shoot the Zombirds. These two games both generally fall into the Tower Defense type genre of games.
Defender II by Droidhen is the sequel to the successfully Defender. The main objective of the game is to defend your castle from waves and waves of enemies. To attack, you simply touch and point it to the direction of your targets. It will automatically shoot when your finger is pressed so no need to tap constantly. Aside from it, you will also gain access to spells which can decimate your foes. When enemies reach your castle, the castle's life is lessened. The game is over when it reaches zero.
Each level increases in difficulty and also the number of enemies to defend from. Some levels have bosses which will prove to be an additional challenge. As with its predecessor, you will gain crystals and coins after each level completed. These will enable you to upgrade your weapon. You can upgrade its various stats. Increasing strength will increase your damage. Increasing agility will increase arrow frequency. By unlocking also these stats, you will gain access to more skills and types of crossbow as well. Upgrading the mana tower will increase your mana for spells and it now also shoots your enemies.
New to this version too is the ability to deploy a lava moat before your castle. The lava moat will incinerate and torch all those enemies which fall to it. The largest addition to Defender II is Battle mode. Now you can challenge other players to whoever survives the longest. Defender II is available free on iOS and Android with options to buy virtual currency to upgrade your skills and weapon.
Shoot the Zombirds by IDream is the successor to Shoot the birds. The gameplay involves you as Pumpkin head or boy shooting the undead birds in the sky and saving little pumpkids along the way. You tap to the direction where you will shoot.
Unlike Defender II which does not run out of arrows, this game does. It forces you to focus more on precision and timing rather than just careless shooting. You will not lose an arrow when you hit a target but will be lost when you miss. The level is over when you reach the number of pumpkids you can afford to lose.
There are fast and slow birds. Aside from birds carrying pumpkids, there are flying skulls which you can hit for gold coins. These gold coins can be used to purchase upgrades such as one time use powerups such rain of arrows or freezing all enemies on screen. You can use them also to increase the amount of arrows and the number of pumpkids you can afford to lose. Costumes are also available to be purchased if you want to change the look of your character.
Overall, Shoot the zombirds is another solid game. The main appeal of it would be its simple polished gameplay and presentation. Its theme is unique and differs from the old usual knights and dragons. This game is also available free on both iOS and Android with options to buy instant gold coins.