diff --git a/docs/README.md b/docs/README.md
index 9736002..f8cb78a 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -13,7 +13,7 @@ Parse and serialize minecraft packets, plus authentication and encryption.
 
  * Supports Minecraft PC version 1.7.10, 1.8.8, 1.9 (15w40b, 1.9, 1.9.1-pre2, 1.9.2, 1.9.4),
   1.10 (16w20a, 1.10-pre1, 1.10, 1.10.1, 1.10.2), 1.11 (16w35a, 1.11, 1.11.2), 1.12 (17w15a, 17w18b, 1.12-pre4, 1.12, 1.12.1, 1.12.2), and 1.13 (17w50a, 1.13, 1.13.1, 1.13.2-pre1, 1.13.2-pre2, 1.13.2), 1.14 (1.14, 1.14.1, 1.14.3, 1.14.4)
-  , 1.15 (1.15, 1.15.1, 1.15.2) and 1.16 (20w13b, 20w14a, 1.16-rc1, 1.16, 1.16.1, 1.16.2, 1.16.3, 1.16.4, 1.16.5), 1.17 (21w07a, 1.17, 1.17.1), 1.18 (1.18, 1.18.1 and 1.18.2), 1.19 (1.19, 1.19.1, 1.19.2, 1.19.3, 1.19.4, 1.20, 1.20.1, 1.20.2, 1.20.3, 1.20.4, 1.20.5, 1.20.6, 1.21.1)
+  , 1.15 (1.15, 1.15.1, 1.15.2) and 1.16 (20w13b, 20w14a, 1.16-rc1, 1.16, 1.16.1, 1.16.2, 1.16.3, 1.16.4, 1.16.5), 1.17 (21w07a, 1.17, 1.17.1), 1.18 (1.18, 1.18.1 and 1.18.2), 1.19 (1.19, 1.19.1, 1.19.2, 1.19.3, 1.19.4), 1.20 (1.20, 1.20.1, 1.20.2, 1.20.3, 1.20.4, 1.20.5, 1.20.6), 1.21 (1.21, 1.21.1, 1.21.3)
  * Parses all packets and emits events with packet fields as JavaScript
    objects.
  * Send a packet by supplying fields as a JavaScript object.
diff --git a/src/datatypes/compiler-minecraft.js b/src/datatypes/compiler-minecraft.js
index ba4db3e..864b269 100644
--- a/src/datatypes/compiler-minecraft.js
+++ b/src/datatypes/compiler-minecraft.js
@@ -1,3 +1,4 @@
+/* eslint-disable no-return-assign */
 const UUID = require('uuid-1345')
 const minecraft = require('./minecraft')
 
@@ -41,7 +42,7 @@ module.exports = {
       code += '}'
       return compiler.wrapCode(code)
     }],
-    arrayWithLengthOffset: ['parametrizable', (compiler, array) => {
+    arrayWithLengthOffset: ['parametrizable', (compiler, array) => { // TODO: remove
       let code = ''
       if (array.countType) {
         code += 'const { value: count, size: countSize } = ' + compiler.callType(array.countType) + '\n'
@@ -61,6 +62,56 @@ module.exports = {
       code += '}\n'
       code += 'return { value: data, size }'
       return compiler.wrapCode(code)
+    }],
+    bitflags: ['parametrizable', (compiler, { type, flags, shift, big }) => {
+      let fstr = JSON.stringify(flags)
+      if (Array.isArray(flags)) {
+        fstr = '{'
+        for (const [k, v] of Object.entries(flags)) fstr += `"${v}": ${big ? (1n << BigInt(k)) : (1 << k)}` + (big ? 'n,' : ',')
+        fstr += '}'
+      } else if (shift) {
+        fstr = '{'
+        for (const key in flags) fstr += `"${key}": ${1 << flags[key]},`
+        fstr += '}'
+      }
+      return compiler.wrapCode(`
+        const { value: _value, size } = ${compiler.callType(type, 'offset')}
+        const value = { _value }
+        const flags = ${fstr}
+        for (const key in flags) {
+          value[key] = (_value & flags[key]) == flags[key]
+        }
+        return { value, size }
+      `.trim())
+    }],
+    registryEntryHolder: ['parametrizable', (compiler, opts) => {
+      return compiler.wrapCode(`
+const { value: n, size: nSize } = ${compiler.callType('varint')}
+if (n !== 0) {
+  return { value: { ${opts.baseName}: n - 1 }, size: nSize }
+} else {
+  const holder = ${compiler.callType(opts.otherwise.type)}
+  return { value: { ${opts.otherwise.name}: holder.data }, size: nSize + holder.size }
+}
+      `.trim())
+    }],
+    registryEntryHolderSet: ['parametrizable', (compiler, opts) => {
+      return compiler.wrapCode(`
+  const { value: n, size: nSize } = ${compiler.callType('varint')}
+  if (n === 0) {
+    const base = ${compiler.callType(opts.base.type, 'offset + nSize')}
+    return { value: { ${opts.base.name}: base.value }, size: base.size + nSize }
+  } else {
+    const set = []
+    let accSize = nSize
+    for (let i = 0; i < n - 1; i++) {
+      const entry = ${compiler.callType(opts.otherwise.type, 'offset + accSize')}
+      set.push(entry.value)
+      accSize += entry.size
+    }
+    return { value: { ${opts.otherwise.name}: set }, size: accSize }
+  }
+    `.trim())
     }]
   },
   Write: {
@@ -106,6 +157,58 @@ module.exports = {
       code += '}\n'
       code += 'return offset'
       return compiler.wrapCode(code)
+    }],
+    bitflags: ['parametrizable', (compiler, { type, flags, shift, big }) => {
+      let fstr = JSON.stringify(flags)
+      if (Array.isArray(flags)) {
+        fstr = '{'
+        for (const [k, v] of Object.entries(flags)) fstr += `"${v}": ${big ? (1n << BigInt(k)) : (1 << k)}` + (big ? 'n,' : ',')
+        fstr += '}'
+      } else if (shift) {
+        fstr = '{'
+        for (const key in flags) fstr += `"${key}": ${1 << flags[key]},`
+        fstr += '}'
+      }
+      return compiler.wrapCode(`
+        const flags = ${fstr}
+        let val = value._value ${big ? '|| 0n' : ''}
+        for (const key in flags) {
+          if (value[key]) val |= flags[key]
+        }
+        return (ctx.${type})(val, buffer, offset)
+      `.trim())
+    }],
+    registryEntryHolder: ['parametrizable', (compiler, opts) => {
+      const baseName = `value.${opts.baseName}`
+      const otherwiseName = `value.${opts.otherwise.name}`
+      return compiler.wrapCode(`
+if (${baseName}) {
+  offset = ${compiler.callType(`${baseName} + 1`, 'varint')}
+} else if (${otherwiseName}) {
+  offset = ${compiler.callType(`${otherwiseName}`, opts.otherwise.type)}
+} else {
+  throw new Error('registryEntryHolder type requires "${baseName}" or "${otherwiseName}" fields to be set')
+}
+return offset
+      `.trim())
+    }],
+    registryEntryHolderSet: ['parametrizable', (compiler, opts) => {
+      const baseName = `value.${opts.base.name}`
+      const otherwiseName = `value.${opts.otherwise.name}`
+      return compiler.wrapCode(`
+if (${baseName}) {
+  offset = ${compiler.callType(0, 'varint')}
+  offset = ${compiler.callType(`${baseName}`, opts.base.type)}
+} else if (${otherwiseName}) {
+  offset = ${compiler.callType(`${otherwiseName}.length + 1`, 'varint')}
+  for (let i = 0; i < ${otherwiseName}.length; i++) {
+    offset = ${compiler.callType(`${otherwiseName}[i]`, opts.otherwise.type)}
+  }
+} else {
+  throw new Error('registryEntryHolder type requires "${opts.base.name}" or "${opts.otherwise.name}" fields to be set')
+}
+return offset
+    `.trim())
     }]
   },
   SizeOf: {
@@ -149,6 +252,60 @@ module.exports = {
       }
       code += 'return size'
       return compiler.wrapCode(code)
+    }],
+    bitflags: ['parametrizable', (compiler, { type, flags, shift, big }) => {
+      let fstr = JSON.stringify(flags)
+      if (Array.isArray(flags)) {
+        fstr = '{'
+        for (const [k, v] of Object.entries(flags)) fstr += `"${v}": ${big ? (1n << BigInt(k)) : (1 << k)}` + (big ? 'n,' : ',')
+        fstr += '}'
+      } else if (shift) {
+        fstr = '{'
+        for (const key in flags) fstr += `"${key}": ${1 << flags[key]},`
+        fstr += '}'
+      }
+      return compiler.wrapCode(`
+        const flags = ${fstr}
+        let val = value._value ${big ? '|| 0n' : ''}
+        for (const key in flags) {
+          if (value[key]) val |= flags[key]
+        }
+        return (ctx.${type})(val)
+      `.trim())
+    }],
+    registryEntryHolder: ['parametrizable', (compiler, opts) => {
+      const baseName = `value.${opts.baseName}`
+      const otherwiseName = `value.${opts.otherwise.name}`
+      return compiler.wrapCode(`
+let size = 0
+if (${baseName}) {
+  size += ${compiler.callType(`${baseName} + 1`, 'varint')}
+} else if (${otherwiseName}) {
+  size += ${compiler.callType(`${otherwiseName}`, opts.otherwise.type)}
+} else {
+  throw new Error('registryEntryHolder type requires "${baseName}" or "${otherwiseName}" fields to be set')
+}
+return size
+      `.trim())
+    }],
+    registryEntryHolderSet: ['parametrizable', (compiler, opts) => {
+      const baseName = `value.${opts.base.name}`
+      const otherwiseName = `value.${opts.otherwise.name}`
+      return compiler.wrapCode(`
+let size = 0
+if (${baseName}) {
+  size += ${compiler.callType(0, 'varint')}
+  size += ${compiler.callType(`${baseName}`, opts.base.type)}
+} else if (${otherwiseName}) {
+  size += ${compiler.callType(`${otherwiseName}.length + 1`, 'varint')}
+  for (let i = 0; i < ${otherwiseName}.length; i++) {
+    size += ${compiler.callType(`${otherwiseName}[i]`, opts.otherwise.type)}
+  }
+} else {
+  throw new Error('registryEntryHolder type requires "${opts.base.name}" or "${opts.otherwise.name}" fields to be set')
+}
+return size
+      `.trim())
     }]
   }
 }
diff --git a/src/version.js b/src/version.js
index 327c242..29d71e7 100644
--- a/src/version.js
+++ b/src/version.js
@@ -2,5 +2,5 @@
 
 module.exports = {
   defaultVersion: '1.21.1',
-  supportedVersions: ['1.7', '1.8.8', '1.9.4', '1.10.2', '1.11.2', '1.12.2', '1.13.2', '1.14.4', '1.15.2', '1.16.5', '1.17.1', '1.18.2', '1.19', '1.19.2', '1.19.3', '1.19.4', '1.20', '1.20.1', '1.20.2', '1.20.4', '1.20.6', '1.21.1']
+  supportedVersions: ['1.7', '1.8.8', '1.9.4', '1.10.2', '1.11.2', '1.12.2', '1.13.2', '1.14.4', '1.15.2', '1.16.5', '1.17.1', '1.18.2', '1.19', '1.19.2', '1.19.3', '1.19.4', '1.20', '1.20.1', '1.20.2', '1.20.4', '1.20.6', '1.21.1', '1.21.3']
 }
diff --git a/test/benchmark.js b/test/benchmark.js
index a461037..1d24cd7 100644
--- a/test/benchmark.js
+++ b/test/benchmark.js
@@ -5,17 +5,18 @@ const ITERATIONS = 10000
 const mc = require('../')
 const states = mc.states
 
-const testDataWrite = [
-  { name: 'keep_alive', params: { keepAliveId: 957759560 } },
-  // TODO: 1.19+ `chat` -> `player_chat` feature toggle
-  // { name: 'chat', params: { message: '<Bob> Hello World!' } },
-  { name: 'position_look', params: { x: 6.5, y: 65.62, stance: 67.24, z: 7.5, yaw: 0, pitch: 0, onGround: true } }
-  // TODO: add more packets for better quality data
-]
-
 for (const supportedVersion of mc.supportedVersions) {
   const mcData = require('minecraft-data')(supportedVersion)
   const version = mcData.version
+  const positionFlags = mcData.isNewerOrEqualTo('1.21.3') ? { flags: { onGround: true, hasHorizontalCollision: false } } : { onGround: true }
+  const testDataWrite = [
+    { name: 'keep_alive', params: { keepAliveId: 957759560 } },
+    // TODO: 1.19+ `chat` -> `player_chat` feature toggle
+    // { name: 'chat', params: { message: '<Bob> Hello World!' } },
+    { name: 'position_look', params: { x: 6.5, y: 65.62, stance: 67.24, z: 7.5, yaw: 0, pitch: 0, ...positionFlags } }
+    // TODO: add more packets for better quality data
+  ]
+
   describe('benchmark ' + supportedVersion + 'v', function () {
     this.timeout(60 * 1000)
     const inputData = []
diff --git a/test/clientTest.js b/test/clientTest.js
index 67eb8ec..ef46d34 100644
--- a/test/clientTest.js
+++ b/test/clientTest.js
@@ -59,7 +59,8 @@ for (const supportedVersion of mc.supportedVersions) {
             'server-port': PORT,
             motd: 'test1234',
             'max-players': 120,
-            // 'level-type': 'flat',
+            'level-type': 'flat',
+            'generate-structures': 'false', // 12m
             'use-native-transport': 'false' // java 16 throws errors without this, https://www.spigotmc.org/threads/unable-to-access-address-of-buffer.311602
           }, (err) => {
             if (err) reject(err)
@@ -191,7 +192,6 @@ for (const supportedVersion of mc.supportedVersions) {
             }
           } else {
             // 1.19+
-            console.log('Chat Message', data)
             const sender = JSON.parse(data.senderName)
             const msgPayload = data.formattedMessage ? JSON.parse(data.formattedMessage) : data.plainMessage
             const plainMessage = client.parseMessage(msgPayload).toString()
diff --git a/test/packetTest.js b/test/packetTest.js
index 534d28e..7f89b95 100644
--- a/test/packetTest.js
+++ b/test/packetTest.js
@@ -57,7 +57,32 @@ const nbtValue = {
 
 function getFixedPacketPayload (version, packetName) {
   if (packetName === 'declare_recipes') {
-    if (version['>=']('1.20.5')) {
+    if (version['>=']('1.21.3')) {
+      return {
+        recipes: [
+          {
+            name: 'minecraft:campfire_input',
+            items: [
+              903,
+              976
+            ]
+          }
+        ],
+        stoneCutterRecipes: [
+          {
+            input: {
+              ids: [
+                6
+              ]
+            },
+            slotDisplay: {
+              type: 'item_stack',
+              data: slotValue
+            }
+          }
+        ]
+      }
+    } else if (version['>=']('1.20.5')) {
       return {
         recipes: [
           {
@@ -241,6 +266,13 @@ const values = {
       suggestionType: 'minecraft:summonable_entities'
     }
   },
+  bitflags: function (typeArgs, context) {
+    const results = {}
+    Object.keys(typeArgs.flags).forEach(function (index) {
+      results[typeArgs.flags[index]] = true
+    })
+    return results
+  },
   soundSource: 'master',
   packedChunkPos: {
     x: 10,
@@ -263,7 +295,49 @@ const values = {
     isDebug: false,
     isFlat: false,
     portalCooldown: 0
-  }
+  },
+  MovementFlags: {
+    onGround: true,
+    hasHorizontalCollision: false
+  },
+  ContainerID: 0,
+  PositionUpdateRelatives: {
+    x: true,
+    y: true,
+    z: true,
+    yaw: true,
+    pitch: true,
+    dx: true,
+    dy: true,
+    dz: true,
+    yawDelta: true
+  },
+  RecipeDisplay: {
+    type: 'stonecutter',
+    data: {
+      ingredient: { type: 'empty' },
+      result: { type: 'empty' },
+      craftingStation: { type: 'empty' }
+    }
+  },
+  SlotDisplay: { type: 'empty' },
+  game_profile: {
+    name: 'test',
+    properties: [{
+      key: 'foo',
+      value: 'bar'
+    }]
+  },
+  optvarint: 1,
+  chat_session: {
+    uuid: '00112233-4455-6677-8899-aabbccddeeff',
+    publicKey: {
+      expireTime: 30,
+      keyBytes: [],
+      keySignature: []
+    }
+  },
+  IDSet: { ids: [2, 5] }
 }
 
 function getValue (_type, packet) {